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Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2019	Oct. 31, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-37976
Entity Registrant Name	Southwest Gas Holdings, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-3881866
Entity Address, Address Line One	5241 Spring Mountain Road
Entity Address, Address Line Two	Post Office Box 98510
Entity Address, City or Town	Las Vegas,
Entity Address, State or Province	NV
Entity Address, Postal Zip Code	89193-8510
City Area Code	(702)
Local Phone Number	876-7237
Title of 12(b) Security	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value
Trading Symbol	SWX
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		54,626,240
Entity Central Index Key	0001692115
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Southwest Gas Corporation
Entity Information [Line Items]
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Entity File Number	1-7850
Entity Registrant Name	Southwest Gas Corporation
Entity Incorporation, State or Country Code	CA
Entity Tax Identification Number	88-0085720
Entity Address, Address Line One	5241 Spring Mountain Road
Entity Address, Address Line Two	Post Office Box 98510
Entity Address, City or Town	Las Vegas,
Entity Address, State or Province	NV
Entity Address, Postal Zip Code	89193-8510
City Area Code	(702)
Local Phone Number	876-7237
Trading Symbol	SWX
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0000092416
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Utility plant:
Gas plant	$ 7,550,855	$ 7,134,239
Less: accumulated depreciation	(2,303,864)	(2,234,029)
Construction work in progress	288,573	193,028
Net utility plant	5,535,564	5,093,238
Other property and investments	768,685	623,551
Current assets:
Cash and cash equivalents	28,480	85,361
Accounts receivable, net of allowances	434,153	413,926
Accrued utility revenue	35,800	77,200
Income taxes receivable	26,611	14,653
Deferred purchased gas costs	49,804	4,928
Prepaid and other current assets	190,554	243,701
Total current assets	765,402	839,769
Noncurrent assets:
Goodwill	339,948	359,045
Deferred income taxes	896	1,264
Deferred charges and other assets	429,716	440,862
Total noncurrent assets	770,560	801,171
Total assets	7,840,211	7,357,729
Capitalization:
Common stock, $1 par (authorized - 120,000,000 shares; issued and outstanding - 54,624,090 and 53,026,848 shares)	56,254	54,656
Additional paid-in capital	1,437,733	1,305,769
Accumulated other comprehensive income (loss), net	(47,775)	(52,668)
Retained earnings	977,498	944,285
Total Southwest Gas Holdings, Inc. equity	2,423,710	2,252,042
Noncontrolling interest	0	(452)
Total equity	2,423,710	2,251,590
Redeemable noncontrolling interest	84,354	81,831
Long-term debt, less current maturities	2,462,116	2,107,258
Total capitalization	4,970,180	4,440,679
Current liabilities:
Current maturities of long-term debt	38,165	33,060
Short-term debt	30,000	152,000
Accounts payable	188,896	248,993
Customer deposits	68,897	67,940
Income taxes payable	1,319	1,083
Accrued general taxes	52,361	43,560
Accrued interest	34,745	21,369
Deferred purchased gas costs	88,030	79,762
Other current liabilities	279,931	290,878
Total current liabilities	782,344	938,645
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	577,928	529,201
Accumulated removal costs	392,000	383,000
Other deferred credits and other long-term liabilities	1,117,759	1,066,204
Total deferred income taxes and other credits	2,087,687	1,978,405
Total capitalization and liabilities	7,840,211	7,357,729
Southwest Gas Corporation
Utility plant:
Gas plant	7,550,855	7,134,239
Less: accumulated depreciation	(2,303,864)	(2,234,029)
Construction work in progress	288,573	193,028
Net utility plant	5,535,564	5,093,238
Other property and investments	127,774	116,146
Current assets:
Cash and cash equivalents	16,811	31,962
Accounts receivable, net of allowances	73,530	140,057
Accrued utility revenue	35,800	77,200
Income taxes receivable	26,663	13,444
Deferred purchased gas costs	49,804	4,928
Prepaid and other current assets	171,402	229,562
Total current assets	374,010	497,153
Noncurrent assets:
Goodwill	10,095	10,095
Deferred charges and other assets	410,512	424,952
Total noncurrent assets	420,607	435,047
Total assets	6,457,955	6,141,584
Capitalization:
Common stock, $1 par (authorized - 120,000,000 shares; issued and outstanding - 54,624,090 and 53,026,848 shares)	49,112	49,112
Additional paid-in capital	1,194,745	1,065,242
Accumulated other comprehensive income (loss), net	(45,287)	(49,049)
Retained earnings	731,036	717,155
Total Southwest Gas Holdings, Inc. equity	1,929,606	1,782,460
Total equity	1,929,606
Long-term debt, less current maturities	2,115,870	1,818,669
Total capitalization	4,045,476	3,601,129
Current liabilities:
Short-term debt	30,000	152,000
Accounts payable	94,130	184,982
Customer deposits	68,897	67,940
Accrued general taxes	52,361	43,560
Accrued interest	34,623	20,243
Deferred purchased gas costs	88,030	79,762
Payable to parent	270	472
Other current liabilities	114,893	94,136
Total current liabilities	483,204	643,095
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	527,544	490,458
Accumulated removal costs	392,000	383,000
Other deferred credits and other long-term liabilities	1,009,731	1,023,902
Total deferred income taxes and other credits	1,929,275	1,897,360
Total capitalization and liabilities	$ 6,457,955	$ 6,141,584

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Common stock, par (in USD per share)	$ 1	$ 1
Common stock, authorized (in shares)	120,000,000	60,000,000
Common stock, issued (in shares)		53,026,848
Common stock, outstanding (in shares)	54,624,090	53,026,848

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating revenues:
Gas operating revenues	$ 209,980	$ 217,523	$ 989,368	$ 987,515	$ 1,359,581	$ 1,354,000
Utility infrastructure services revenues	515,250	450,623	1,282,412	1,105,844	1,698,853	1,479,792
Total operating revenues	725,230	668,146	2,271,780	2,093,359	3,058,434	2,833,792
Operating expenses:
Net cost of gas sold	35,068	49,903	292,854	319,101	393,141	412,307
Operations and maintenance	109,652	105,508	321,190	313,294	414,289	406,137
Depreciation and amortization	75,370	62,156	223,251	185,941	286,522	247,803
Taxes other than income taxes	15,308	15,036	46,640	44,959	61,579	59,580
Utility infrastructure services expenses	451,574	395,862	1,154,238	1,007,485	1,534,442	1,349,862
Total operating expenses	686,972	628,465	2,038,173	1,870,780	2,689,973	2,475,689
Operating income (loss)	38,258	39,681	233,607	222,579	368,461	358,103
Other income and (expenses):
Net interest deductions	(27,434)	(24,548)	(80,662)	(70,831)	(106,502)	(92,032)
Other income (deductions)	(1,158)	889	6,827	(6,151)	(4,448)	(6,401)
Total other income and (expenses)	(28,592)	(23,659)	(73,835)	(76,982)	(110,950)	(98,433)
Income (loss) before income taxes	9,666	16,022	159,772	145,597	257,511	259,670
Income tax expense (benefit)	3,141	3,691	35,031	33,421	63,294	51,098
Net income	6,525	12,331	124,741	112,176	194,217	208,572
Net income (loss) attributable to noncontrolling interests	1,172	0	2,523	(797)	2,695	(866)
Net income attributable to Southwest Gas Holdings, Inc.	$ 5,353	$ 12,331	$ 122,218	$ 112,973	$ 191,522	$ 209,438
Basic earnings per share (in USD per share)	$ 0.10	$ 0.25	$ 2.26	$ 2.31	$ 3.60	$ 4.30
Diluted earnings per share (in USD per share)	$ 0.10	$ 0.25	$ 2.26	$ 2.31	$ 3.59	$ 4.29
Average number of common shares (in shares)	54,670	49,493	53,996	48,916	53,219	48,728
Average shares (assuming dilution) (in shares)	54,748	49,553	54,063	48,968	53,287	48,781
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 209,980	$ 217,523	$ 989,368	$ 987,515	$ 1,359,581	$ 1,354,000
Operating expenses:
Net cost of gas sold	35,068	49,903	292,854	319,101	393,141	412,307
Operations and maintenance	109,039	104,657	319,572	312,055	412,330	404,549
Depreciation and amortization	52,372	47,924	159,327	145,549	205,594	193,828
Taxes other than income taxes	15,308	15,036	46,640	44,959	61,579	59,580
Total operating expenses	211,787	217,520	818,393	821,664	1,072,644	1,070,264
Operating income (loss)	(1,807)	3	170,975	165,851	286,937	283,736
Other income and (expenses):
Net interest deductions	(23,619)	(20,399)	(70,063)	(59,803)	(92,000)	(77,914)
Other income (deductions)	(1,353)	836	6,185	(5,861)	(5,194)	(6,425)
Total other income and (expenses)	(24,972)	(19,563)	(63,878)	(65,664)	(97,194)	(84,339)
Income (loss) before income taxes	(26,779)	(19,560)	107,097	100,187	189,743	199,397
Income tax expense (benefit)	(6,767)	(5,890)	20,351	20,886	43,456	45,714
Net income	(20,012)	(13,670)	86,746	79,301	146,287	153,683
Net income attributable to Southwest Gas Holdings, Inc.	$ (20,012)	$ (13,670)	$ 86,746	$ 79,301	$ 146,287	$ 153,683

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net income (loss)	$ 6,525	$ 12,331	$ 124,741	$ 112,176	$ 194,217	$ 208,572
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	0	0	(15,524)	(32,701)
Amortization of prior service cost	241	254	724	762	977	969
Amortization of net actuarial loss	4,442	6,387	13,325	19,161	19,713	23,105
Regulatory adjustment	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Net defined benefit pension plans	618	895	1,856	2,687	3,952	(2,606)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,906	1,907	2,540	2,426
Net forward-starting interest rate swaps	635	636	1,906	1,907	2,540	2,426
Foreign currency translation adjustments	(447)	599	1,131	(1,002)	(877)	(1,092)
Total other comprehensive income (loss), net of tax	806	2,130	4,893	3,592	5,615	(1,272)
Comprehensive income (loss)	7,331	14,461	129,634	115,768	199,832	207,300
Comprehensive income (loss) attributable to noncontrolling interests	1,172	0	2,523	(797)	2,695	(866)
Comprehensive income attributable to Southwest Gas Holdings, Inc.	6,159	14,461	127,111	116,565	197,137	208,166
Southwest Gas Corporation
Net income (loss)	(20,012)	(13,670)	86,746	79,301	146,287	153,683
Defined benefit pension plans:
Net actuarial gain (loss)	0	0	0	0	(15,524)	(32,701)
Amortization of prior service cost	241	254	724	762	977	969
Amortization of net actuarial loss	4,442	6,387	13,325	19,161	19,713	23,105
Regulatory adjustment	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Net defined benefit pension plans	618	895	1,856	2,687	3,952	(2,606)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income	635	636	1,906	1,907	2,540	2,426
Net forward-starting interest rate swaps	635	636	1,906	1,907	2,540	2,426
Total other comprehensive income (loss), net of tax	1,253	1,531	3,762	4,594	6,492	(180)
Comprehensive income (loss)	$ (18,759)	$ (12,139)	$ 90,508	$ 83,895	$ 152,779	$ 153,503

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
CASH FLOW FROM OPERATING ACTIVITIES:
Net income (loss)	$ 124,741	$ 112,176	$ 194,217	$ 208,572
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	223,251	185,941	286,522	247,803
Deferred income taxes	46,099	36,210	60,930	50,190
Changes in current assets and liabilities:
Accounts receivable, net of allowances	(19,615)	(1,659)	(33,818)	(27,276)
Accrued utility revenue	41,400	43,600	(1,200)	(500)
Deferred purchased gas costs	(36,608)	100,763	(54,797)	84,282
Accounts payable	(46,079)	(48,618)	14,317	(1,886)
Accrued taxes	(2,841)	(9,840)	(4,956)	(12,417)
Other current assets and liabilities	74,048	1,245	18,730	(50,002)
Gains on sale	(3,157)	(997)	(3,863)	(3,741)
Changes in undistributed stock compensation	6,067	4,686	7,492	6,375
Equity AFUDC	(3,179)	(1,034)	(5,772)	(1,253)
Changes in other assets and deferred charges	(15,855)	(10,497)	(11,096)	(18,296)
Changes in other liabilities and deferred credits	(9,786)	(4,583)	33,243	(3,747)
Net cash provided by operating activities	378,486	407,393	499,949	478,104
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(719,386)	(560,165)	(925,135)	(733,816)
Acquisition of businesses, net of cash acquired	(19,533)	(4,209)	(266,697)	(98,413)
Changes in customer advances	15,049	11,051	17,461	13,325
Miscellaneous inflows	12,862	3,827	13,376	11,312
Net cash used in investing activities	(711,008)	(549,496)	(1,160,995)	(807,592)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	129,341	92,234	391,509	121,826
Dividends paid	(86,345)	(74,535)	(112,050)	(98,162)
Issuance of long-term debt, net	482,614	480,993	566,793	783,748
Retirement of long-term debt	(127,175)	(143,757)	(221,176)	(382,486)
Change in short-term debt	(122,000)	(183,000)	(1,500)	(79,000)
Principal payments on finance lease obligations	(161)	(422)	(387)	(606)
Withholding remittance - share-based compensation	(1,858)	(2,880)	(2,088)	(2,880)
Other	1,167	(1,121)	(456)	(3,091)
Net cash provided by financing activities	275,583	167,512	620,645	339,349
Effects of currency translation on cash and cash equivalents	58	139	(289)	157
Change in cash and cash equivalents	(56,881)	25,548	(40,690)	10,018
Cash and cash equivalents at beginning of period	85,361	43,622	69,170	59,152
Cash and cash equivalents at end of period	28,480	69,170	28,480	69,170
Supplemental information:
Interest paid, net of amounts capitalized	62,165	49,568	99,159	75,740
Income taxes paid (received)	371	18,261	(16,669)	20,247
Southwest Gas Corporation
CASH FLOW FROM OPERATING ACTIVITIES:
Net income (loss)	86,746	79,301	146,287	153,683
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	159,327	145,549	205,594	193,828
Deferred income taxes	35,899	33,239	45,659	55,787
Changes in current assets and liabilities:
Accounts receivable, net of allowances	66,527	49,654	(3,436)	(2,066)
Accrued utility revenue	41,400	43,600	(1,200)	(500)
Deferred purchased gas costs	(36,608)	100,763	(54,797)	84,282
Accounts payable	(77,311)	(53,217)	(686)	(2,700)
Accrued taxes	(4,419)	(16,026)	(7,125)	(9,735)
Other current assets and liabilities	87,869	(35,154)	31,579	(81,333)
Changes in undistributed stock compensation	4,710	4,269	5,796	5,558
Equity AFUDC	(3,179)	(1,034)	(5,772)	(1,253)
Changes in other assets and deferred charges	(21,098)	(11,025)	(17,122)	(19,082)
Changes in other liabilities and deferred credits	(10,357)	7,550	19,762	8,208
Net cash provided by operating activities	329,506	347,469	364,539	384,677
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(587,405)	(486,037)	(784,237)	(651,022)
Changes in customer advances	15,049	11,051	17,461	13,325
Miscellaneous inflows	(51)	1,316	(1,353)	1,650
Net cash used in investing activities	(572,407)	(473,670)	(768,129)	(636,047)
CASH FLOW FROM FINANCING ACTIVITIES:
Contributions from parent	126,186	90,644	149,091	120,344
Dividends paid	(71,000)	(65,000)	(93,000)	(86,000)
Issuance of long-term debt, net	297,222	297,495	297,222	297,495
Change in short-term debt	(122,000)	(182,000)	21,000	(74,000)
Withholding remittance - share-based compensation	(1,857)	(2,880)	(2,087)	(2,880)
Other	(801)	(939)	(890)	(991)
Net cash provided by financing activities	227,750	137,320	371,336	253,968
Change in cash and cash equivalents	(15,151)	11,119	(32,254)	2,598
Cash and cash equivalents at beginning of period	31,962	37,946	49,065	46,467
Cash and cash equivalents at end of period	16,811	49,065	16,811	49,065
Supplemental information:
Interest paid, net of amounts capitalized	51,720	42,986	82,539	67,025
Income taxes paid (received)	$ (22)	$ 11,286	$ (17,164)	$ 3,428

CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Southwest Gas Corporation	Common Stock	Common Stock Southwest Gas Corporation	Additional paid-in capital	Additional paid-in capital Southwest Gas Corporation	Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) Southwest Gas Corporation	Retained Earnings	Retained Earnings Southwest Gas Corporation	Southwest Gas Holdings, Inc.	Non-controlling Interest
Beginning balance (in shares) at Dec. 31, 2017			48,090,000	47,482,000
Beginning balance at Dec. 31, 2017			$ 49,720	$ 49,112	$ 955,332	$ 948,767	$ (47,682)	$ (47,073)	$ 857,398	$ 659,193		$ (2,365)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,333,000
Common stock issuances			$ 1,333		93,218
Net income (loss)									112,973	79,301		(797)
Change in ownership of noncontrolling interest					(2,710)							2,710
Foreign currency exchange translation adjustment							(1,002)
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							2,687	2,687
FSIRS amounts reclassified to net income, net of tax	$ 1,907	$ 1,907					1,907	1,907
Reclassification of excess deferred taxes							(9,300)	(9,300)	9,300	9,300
Share-based compensation						1,899				(510)
Dividends declared									(76,941)	(66,000)
Contributions from Southwest Gas Holdings, Inc.						90,644
Ending balance (in shares) at Sep. 30, 2018			49,423,000	47,482,000
Ending balance at Sep. 30, 2018	$ 1,945,781	1,719,927	$ 51,053	$ 49,112	1,045,840	1,041,310	(53,390)	(51,779)	902,730	681,284	$ 1,946,233	(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.56
Beginning balance (in shares) at Jun. 30, 2018			49,126,000	47,482,000
Beginning balance at Jun. 30, 2018			$ 50,756	$ 49,112	1,021,508	1,006,065	(55,520)	(53,310)	916,275	717,126		(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			297,000
Common stock issuances			$ 297		24,332
Net income (loss)									12,331	(13,670)		0
Change in ownership of noncontrolling interest					0							0
Foreign currency exchange translation adjustment							599
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							895	895
FSIRS amounts reclassified to net income, net of tax	$ 636	636					636	636
Reclassification of excess deferred taxes							0	0	0	0
Share-based compensation						1,197				(172)
Dividends declared									(25,876)	(22,000)
Contributions from Southwest Gas Holdings, Inc.						34,048
Ending balance (in shares) at Sep. 30, 2018			49,423,000	47,482,000
Ending balance at Sep. 30, 2018	$ 1,945,781	1,719,927	$ 51,053	$ 49,112	1,045,840	1,041,310	(53,390)	(51,779)	902,730	681,284	1,946,233	(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.52
FSIRS amounts reclassified to net income, net of tax	$ 2,540	2,540
Ending balance (in shares) at Sep. 30, 2019	54,624,090		54,624,000	47,482,000
Ending balance at Sep. 30, 2019	$ 2,423,710	1,929,606	$ 56,254	$ 49,112	1,437,733	1,194,745	(47,775)	(45,287)	977,498	731,036	2,423,710	0
Beginning balance (in shares) at Dec. 31, 2018	53,026,848		53,026,000	47,482,000
Beginning balance at Dec. 31, 2018	$ 2,251,590		$ 54,656	$ 49,112	1,305,769	1,065,242	(52,668)	(49,049)	944,285	717,155		(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,598,000
Common stock issuances			$ 1,598		132,416
Net income (loss)									122,218	86,746		0
Change in ownership of noncontrolling interest					(452)							452
Foreign currency exchange translation adjustment							1,131
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							1,856	1,856
FSIRS amounts reclassified to net income, net of tax	$ 1,906	1,906					1,906	1,906
Reclassification of excess deferred taxes							0	0	0	0
Share-based compensation						3,317				(465)
Dividends declared									(89,005)	(72,400)
Contributions from Southwest Gas Holdings, Inc.						126,186
Ending balance (in shares) at Sep. 30, 2019	54,624,090		54,624,000	47,482,000
Ending balance at Sep. 30, 2019	$ 2,423,710	1,929,606	$ 56,254	$ 49,112	1,437,733	1,194,745	(47,775)	(45,287)	977,498	731,036	2,423,710	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.635
Beginning balance (in shares) at Jun. 30, 2019			54,321,000	47,482,000
Beginning balance at Jun. 30, 2019			$ 55,951	$ 49,112	1,409,923	1,169,549	(48,581)	(46,540)	1,002,070	776,101		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			303,000
Common stock issuances			$ 303		27,810
Net income (loss)									5,353	(20,012)		0
Change in ownership of noncontrolling interest					0							0
Foreign currency exchange translation adjustment							(447)
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							618	618
FSIRS amounts reclassified to net income, net of tax	$ 635	635					635	635
Reclassification of excess deferred taxes							0	0	0	0
Share-based compensation						1,102				(153)
Dividends declared									(29,925)	(24,900)
Contributions from Southwest Gas Holdings, Inc.						24,094
Ending balance (in shares) at Sep. 30, 2019	54,624,090		54,624,000	47,482,000
Ending balance at Sep. 30, 2019	$ 2,423,710	$ 1,929,606	$ 56,254	$ 49,112	$ 1,437,733	$ 1,194,745	$ (47,775)	$ (45,287)	$ 977,498	$ 731,036	$ 2,423,710	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.545

Background, Organization, and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Background, Organization, and Summary of Significant Accounting Policies

Note 1 – Background, Organization, and Summary of Significant Accounting Policies

Nature of Operations. Southwest Gas Holdings, Inc. is a holding company, owning all of the shares of common stock of Southwest Gas Corporation (“Southwest” or the “natural gas operations” segment) and all of the shares of common stock of Centuri Group, Inc. (“Centuri,” or the “utility infrastructure services” segment). At the annual meeting of shareholders of Southwest Gas Holdings, Inc., held on May 2, 2019, shareholders voted to approve changing the state of incorporation for Southwest Gas Holdings, Inc. from California to Delaware. The reincorporation became effective September 20, 2019.

Southwest is engaged in the business of purchasing, distributing, and transporting natural gas for customers in portions of Arizona, Nevada, and California. Public utility rates, practices, facilities, and service territories of Southwest are subject to regulatory oversight. The timing and amount of rate relief can materially impact results of operations. Natural gas purchases and the timing of related recoveries can materially impact liquidity. Results for the natural gas operations segment are higher during winter periods due to the seasonality incorporated in its regulatory rate structures.

Centuri is a comprehensive utility infrastructure services enterprise dedicated to delivering a diverse array of solutions to North America’s gas and electric providers. Centuri derives revenue from installation, replacement, repair, and maintenance of energy distribution systems, and developing industrial construction solutions. Centuri operations are generally conducted under the business names of NPL Construction Co. (“NPL”), NPL Canada Ltd. (“NPL Canada”), New England Utility Constructors, Inc. (“Neuco”), and Linetec Services, LLC (“Linetec”). Utility infrastructure services activity is seasonal in most of Centuri’s operating areas. Peak periods are the summer and fall months in colder climate areas, such as the northeastern and midwestern United States (“U.S.”) and in Canada. In warmer climate areas, such as the southwestern and southeastern U.S., utility infrastructure services activity continues year round. In November 2017, Centuri acquired Neuco, thereby expanding its core services in the northeast region of the U.S. Additionally, in November 2018, Centuri expanded its operations in the southeast region of the U.S. through the acquisition of an 80% interest in Linetec. See Note 12 – Business Acquisitions for more information.

Basis of Presentation. The condensed consolidated financial statements of Southwest Gas Holdings, Inc. and subsidiaries (the “Company”) and Southwest included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The year-end condensed balance sheet data was derived from audited financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) have been condensed or omitted pursuant to such rules and regulations. No substantive change has occurred with regard to the Company’s business segments on the whole, or in the primary businesses comprising those segments as a result of the foregoing acquisitions of Neuco and Linetec.

The preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of management, all adjustments, consisting of normal recurring items and estimates necessary for a fair depiction of results for the interim periods, have been made. It is suggested that these condensed consolidated financial statements be read in conjunction with the consolidated financial statements and the notes thereto included in the 2018 Annual Report to Shareholders, which is incorporated by reference into the 2018 Form 10-K.

Fair Value Measurements. Certain assets and liabilities are reported at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.

U.S. GAAP states that a fair value measurement should be based on the assumptions that market participants would use in pricing the asset or liability and establishes a fair value hierarchy that ranks the inputs used to measure fair value by their reliability. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to fair values derived from unobservable inputs (Level 3 measurements). Financial assets and liabilities are categorized in their entirety based on the lowest level of input that is significant to the fair value measurement. The three levels of the fair value hierarchy are as follows:

Level 1 – quoted prices (unadjusted) in active markets for identical assets or liabilities that a company has the ability to access at the measurement date.

Level 2 – inputs other than quoted prices included within Level 1 that are observable for similar assets or liabilities, either directly or indirectly.

Level 3 – unobservable inputs for the asset or liability. Unobservable inputs are used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date.

The Company primarily used quoted market prices and other observable market pricing information in valuing cash and cash equivalents, derivatives, long-term debt outstanding, and assets of the qualified pension plan and postretirement benefit plans required to be recorded and/or disclosed at fair value.

Other Property and Investments. Other property and investments on the Condensed Consolidated Balance Sheets includes (thousands of dollars):



	September 30, 2019			December 31, 2018
Southwest Gas Corporation:
Net cash surrender value of COLI policies	$	126,142		$	114,405
Other property	1,632			1,741
Total Southwest Gas Corporation	127,774			116,146
Centuri property, equipment, and intangibles	968,013			792,191
Centuri accumulated depreciation/amortization	(345,113		)	(298,939		)
Other property	18,011			14,153
Total Southwest Gas Holdings, Inc.	$	768,685		$	623,551

Included in the table above are the net cash surrender values of company-owned life insurance (“COLI”) policies. These life insurance policies on members of management and other key employees are used by Southwest to indemnify itself against the loss of talent, expertise, and knowledge, as well as to provide indirect funding for certain nonqualified benefit plans.

Cash and Cash Equivalents. For purposes of reporting consolidated cash flows, cash and cash equivalents include cash on hand and financial instruments with original maturities of three months or less. Such investments are carried at cost, which approximates market value. Cash and cash equivalents for Southwest and the Company also include money market fund investments totaling approximately $1.5 million and $10.2 million, respectively, at September 30, 2019, and $18 million and $59.9 million, respectively, at December 31, 2018, which fall within Level 2 of the fair value hierarchy, due to the asset valuation methods used by money market funds.

Typical non-cash investing activities for Southwest include customer advances applied as contributions toward utility construction activity and capital expenditures that were not paid as of quarter end that are included in accounts payable. Amounts related to such activities were immaterial for the periods presented herein. Non-cash investing activities for the twelve months ended September 30, 2019 included $26.2 million of purchase consideration related to the Linetec acquisition by Centuri, in the form of liabilities incurred that remained unpaid as of September 30, 2019; such amounts are included in Other current liabilities on the Condensed Consolidated Balance Sheets of the Company. Also, see Recent Accounting Standards Updates and Note 4 – Leases for information related to right-of-use assets obtained in exchange for lease liabilities, which are non-cash investing and financing activities.

Intercompany Transactions. Centuri recognizes revenues generated from contracts with Southwest (see Note 10 – Segment Information). Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars):



	September 30, 2019		December 31, 2018
Centuri accounts receivable for services provided to Southwest	$	16,757	$	18,830

The accounts receivable balance, revenues, and associated profits are included in the condensed consolidated financial statements of the Company and Southwest and were not eliminated during consolidation in accordance with accounting treatment for rate-regulated entities.

Income Taxes. In 2017, the Tax Cuts and Jobs Act (the “TCJA”) was enacted. The TCJA had significant impacts on the taxation of business entities, including specific provisions related to regulated public utilities. The more significant changes that impacted the Company and Southwest include the reduction in the corporate federal income tax rate from 35% to 21%, and limiting the utilization of net operating losses (“NOLs”) to 80% of taxable income, with the ability to indefinitely carryforward unutilized NOLs to reduce future taxable income.

Prepaid and Other Current Assets. Prepaid and other current assets includes gas pipe materials and operating supplies of $59 million at September 30, 2019 and $56 million at December 31, 2018 (carried at weighted average cost), in addition to $47 million at September 30, 2019 and $74 million at December 31, 2018 related to a regulatory asset associated with the Arizona decoupling mechanism (an alternative revenue program).

Goodwill. Goodwill is assessed as of October 1st each year for impairment, or more frequently, if circumstances indicate an impairment to the carrying value of goodwill may have occurred. Management of the Company and Southwest considered its reporting units and segments and determined that its segments and reporting units remain consistent between periods presented below, and that no change was necessary with regard to the level at which goodwill is assessed for impairment. No impairment was deemed to have occurred in the first nine months of 2019.



(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services			Total Company
December 31, 2018	$	10,095	$	348,950		$	359,045
Measurement-period adjustments - Linetec acquisition (a)	—		(22,179		)	(22,179		)
Foreign currency translation adjustment	—		3,082			3,082
September 30, 2019	$	10,095	$	329,853		$	339,948

(a) See Note 12 – Business Acquisitions for details regarding Linetec measurement-period adjustments.

Other Current Liabilities. Other current liabilities for Southwest include $24.9 million and $23.5 million of dividends declared by Southwest Gas Corporation, but not yet paid to Southwest Gas Holdings, Inc. at September 30, 2019 and December 31, 2018, respectively. In addition, the balances in both periods include amounts payable under regulatory mechanisms in the next twelve months and miscellaneous other accrued liabilities. Amounts included in the Condensed Consolidated Balance Sheets of Southwest Gas Holdings, Inc. for both periods reflect unremitted consideration then outstanding associated with the business acquisition of Linetec.

Other Income (Deductions). The following table provides the composition of significant items included in Other income (deductions) in the Condensed Consolidated Statements of Income (thousands of dollars):



	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30,						September 30,						September 30,
	2019			2018			2019			2018			2019			2018
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	200		$	4,700		$	11,200		$	6,000		$	2,000		$	9,500
Interest income	1,521			1,506			4,940			4,301			6,659			5,237
Equity AFUDC	1,212			448			3,179			1,034			5,772			1,253
Other components of net periodic benefit cost	(3,765		)	(5,265		)	(11,295		)	(15,794		)	(16,560		)	(20,650		)
Miscellaneous income and (expense)	(521		)	(553		)	(1,839		)	(1,402		)	(3,065		)	(1,765		)
Southwest Gas Corporation - total other income (deductions)	(1,353		)	836			6,185			(5,861		)	(5,194		)	(6,425		)
Utility infrastructure services segment:
Interest income	—			4			—			6			82			7
Foreign transaction gain (loss)	(6		)	(91		)	546			258			66			144
Miscellaneous income and (expense)	177			125			23			(595		)	514			(175		)
Centuri - total other income (deductions)	171			38			569			(331		)	662			(24		)
Corporate and administrative	24			15			73			41			84			48
Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	(1,158	)	$	889		$	6,827		$	(6,151	)	$	(4,448	)	$	(6,401	)

Included in the table above is the change in cash surrender values of COLI policies (including net death benefits recognized). Current tax regulations provide for tax-free treatment of life insurance (death benefit) proceeds. Therefore, changes in the cash surrender values of COLI policies, as they progress towards the ultimate death benefits, are also recorded without tax consequences. Refer also to Note 2 – Components of Net Periodic Benefit Cost.

Recent Accounting Standards Updates.

Accounting pronouncements adopted in 2019:

In February 2016, the Financial Accounting Standards Board (“FASB”) issued the update “Leases (Topic 842).” Under the update, lessees were required to recognize a lease liability for the obligation to make lease payments, measured on a discounted basis; and a right-of-use asset for the right to use, or control the use of, a specified asset for the lease term. The Company and Southwest adopted Topic 842 in the first quarter of 2019 through an optional transition method, which was elected, permitting the application of the provisions of the standard at the adoption date, rather than to earlier comparative periods. As a result, the Company and Southwest have not recast prior periods to reflect the adoption of this standard. See Note 4 – Leases.

Accounting pronouncements that will be effective after 2019:

In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13 update “Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The update requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The inputs currently used to estimate credit losses will still be used; however, they may be adapted to reflect the full amount of expected losses. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. All entities may adopt the amendments in this update earlier as of fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Management is evaluating what impact, if any, this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures.

In January 2017, the FASB issued ASU 2017-04 “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” Under the update, an entity will apply a one-step quantitative test as opposed to a two-step test as currently required, and record the amount of goodwill impairment as the excess of a reporting unit's carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment. The amount of any goodwill impairment calculated under the update could vary from the calculation under existing guidance, largely due to the consideration to be given to unrecognized differences between the fair value and carrying values of the other assets and liabilities in the reporting unit under the new guidance. The amendments should be applied on a prospective basis. The update is effective for fiscal and interim periods beginning after December 15, 2019. Early adoption has been permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. Management is evaluating the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures.

In August 2018, the FASB issued ASU 2018-15 “Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract.” The update generally aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement (that is a service contract) with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. Once capitalized, the update requires the entity to expense the amount capitalized over the term of the hosting arrangement, including reasonably certain renewal periods. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption of the amendments in this update is permitted for interim and related annual fiscal periods after December 15, 2018. Management is evaluating the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures.

In August 2018, the FASB issued ASU 2018-14 “Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans.” This update removes disclosures that are no longer considered cost-beneficial, clarifies the specific requirements of disclosures, and adds disclosure requirements identified as relevant. The update applies to all employers that sponsor defined benefit pension or other postretirement plans. The update is effective for fiscal years ending after December 15, 2020. Upon adoption, the Company and Southwest will modify their disclosures to conform to the requirements of the update.

In August 2018, the FASB issued ASU 2018-13 “Fair Value Measurement: Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement.” The update modifies the disclosure requirements on fair value measurements in Topic 820. The update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Upon adoption, the Company and Southwest will modify their disclosures to conform to the requirements of the update, as applicable.

Components of Net Periodic Benefit Cost

9 Months Ended

Sep. 30, 2019

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost

Note 2 – Components of Net Periodic Benefit Cost

Southwest has a noncontributory qualified retirement plan with defined benefits covering substantially all employees and a separate unfunded supplemental retirement plan (“SERP”) which is limited to officers. Southwest also provides postretirement benefits other than pensions (“PBOP”) to its qualified retirees for health care, dental, and life insurance.

The service cost component of net periodic benefit costs included in the table below are components of an overhead loading process associated with the cost of labor. The overhead process ultimately results in allocation of that portion of overall net periodic benefit costs to the same accounts to which productive labor is charged. As a result, service costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets for both the Company and Southwest. The other components of net periodic benefit cost are reflected in Other income (deductions) on the Condensed Consolidated Statements of Income of each entity.



	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	6,466		$	7,139		$	19,398		$	21,417		$	26,536		$	27,265
Interest cost	12,252			11,043			36,755			33,130			47,799			44,652
Expected return on plan assets	(15,061		)	(14,689		)	(45,183		)	(44,066		)	(59,872		)	(57,865		)
Amortization of net actuarial loss	5,589			8,029			16,767			24,086			24,796			30,087
Net periodic benefit cost	$	9,246		$	11,522		$	27,737		$	34,567		$	39,259		$	44,139

	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	66		$	61		$	199		$	183		$	261		$	260
Interest cost	440			415			1,320			1,244			1,734			1,714
Amortization of net actuarial loss	255			375			765			1,126			1,141			1,486
Net periodic benefit cost	$	761		$	851		$	2,284		$	2,553		$	3,136		$	3,460

	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	319		$	368		$	957		$	1,105		$	1,325		$	1,472
Interest cost	761			687			2,285			2,061			2,972			2,869
Expected return on plan assets	(789		)	(929		)	(2,367		)	(2,789		)	(3,296		)	(3,629		)
Amortization of prior service costs	318			334			953			1,002			1,286			1,336
Net periodic benefit cost	$	609		$	460		$	1,828		$	1,379		$	2,287		$	2,048

Revenue

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Revenue

Note 3 – Revenue

The following information about the Company’s revenues is presented by segment. Southwest encompasses one segment – natural gas operations.

Natural Gas Operations Segment:

Gas operating revenues on the Condensed Consolidated Statements of Income of both the Company and Southwest include revenue from contracts with customers, which is shown below, disaggregated by customer type, and various categories of revenue:



	Three Months Ended				Nine Months Ended					Twelve Months Ended
	September 30,				September 30,					September 30,
(Thousands of dollars)	2019		2018		2019			2018		2019			2018
Residential	$	124,169	$	120,249	$	706,270		$	631,562	$	961,928		$	864,128
Small commercial	39,725		40,020		179,519			183,616		250,986			253,330
Large commercial	10,945		11,360		36,030			39,934		49,288			54,462
Industrial/other	3,837		5,390		15,728			17,391		21,826			23,899
Transportation	21,580		19,818		68,297			64,591		90,696			88,115
Revenue from contracts with customers	200,256		196,837		1,005,844			937,094		1,374,724			1,283,934
Alternative revenue program revenues (deferrals)	7,957		9,094		(23,196		)	46,696		(23,913		)	67,017
Other revenues (a)	1,767		11,592		6,720			3,725		8,770			3,049
Total Gas operating revenues	$	209,980	$	217,523	$	989,368		$	987,515	$	1,359,581		$	1,354,000

(a) Comprised of various other revenue impacts, including $(0.8) million during the three months, and $(3.7) million for the nine and twelve months ending September 30, 2019, respectively; and, $(1) million during the three months, and $(13.5) million in both the nine and twelve months ending September 30, 2018 related to tax reform savings reserves/adjustments.

Utility Infrastructure Services Segment:

The following tables display Centuri’s revenue, reflected as Utility infrastructure services revenues on the Condensed Consolidated Statements of Income of the Company, representing revenue from contracts with customers disaggregated by service and contract types:



(Thousands of dollars)	Three Months Ended				Nine Months Ended				Twelve Months Ended
	September 30,				September 30,				September 30,
	2019		2018		2019		2018		2019		2018
Service Types:
Gas infrastructure services	$	364,241	$	355,721	$	885,950	$	849,615	$	1,160,017	$	1,145,629
Electric power infrastructure services	70,610		4,666		184,277		14,062		202,844		19,304
Other	80,399		90,236		212,185		242,167		335,992		314,859
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792



(Thousands of dollars)	Three Months Ended				Nine Months Ended				Twelve Months Ended
	September 30,				September 30,				September 30,
	2019		2018		2019		2018		2019		2018
Contract Types:
Master services agreement	$	410,283	$	348,274	$	1,021,798	$	832,813	$	1,291,397	$	1,101,216
Bid contract	104,967		102,349		260,614		273,031		407,456		378,576
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792

Unit price contracts	$	415,404	$	368,918	$	1,006,577	$	948,593	$	1,316,404	$	1,286,059
Fixed price contracts	37,539		45,461		80,503		44,911		152,890		31,487
Time and materials contracts	62,307		36,244		195,332		112,340		229,559		162,246
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792

The following table provides information about contracts receivable and revenue earned on contracts in progress in excess of billings (contract asset), which are both included within Accounts receivable, net of allowances, as well as amounts billed in excess of revenue earned on contracts (contract liability), which are included in Other current liabilities as of September 30, 2019 and December 31, 2018 on the Company’s Condensed Consolidated Balance Sheets:



(Thousands of dollars)	September 30, 2019		December 31, 2018
Contracts receivable, net	$	238,678	$	186,249
Revenue earned on contracts in progress in excess of billings	121,854		87,520
Amounts billed in excess of revenue earned on contracts	6,136		4,211

The revenue earned on contracts in progress in excess of billings (contract asset) primarily relates to Centuri’s rights to consideration for work completed but not billed and/or approved at the reporting date. These contract assets are transferred to contracts receivable when the rights become unconditional. The amounts billed in excess of revenue earned (contract liability) primarily relates to the advance consideration received from customers for which work has not yet been completed. The change in this contract liability balance from December 31, 2018 to September 30, 2019 is due to revenue recognized of $4.2 million that was included in this item as of January 1, 2019, after which time it became earned and the balance was reduced, and to increases due to cash received, net of revenue recognized during the period related to contracts that commenced during the period.

For contracts that have an original duration of one year or less, Centuri uses the practical expedient applicable to such contracts and does not consider/compute an interest component based on the time value of money. Further, because of the short duration of these contracts, Centuri has not disclosed the transaction price for the remaining performance obligations as of the end of each reporting period or when the Company expects to recognize the revenue.

As of September 30, 2019, Centuri has 53 contracts with an original duration of more than one year. The aggregate amount of the transaction price allocated to the unsatisfied performance obligations of these contracts as of September 30, 2019 was $103.3 million. Centuri expects to recognize the remaining performance obligations over approximately the next two years; however, the timing of that recognition is largely within the control of the customer, including when the necessary equipment and materials required to complete the work are provided by the customer.

Utility infrastructure services contracts receivable consists of the following:



(Thousands of dollars)	September 30, 2019			December 31, 2018
Billed on completed contracts and contracts in progress	$	238,117		$	184,100
Other receivables	1,156			2,588
Contracts receivable, gross	239,273			186,688
Allowance for doubtful accounts	(595		)	(439		)
Contracts receivable, net	$	238,678		$	186,249

Leases

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Leases

Note 4 – Leases

The Company and Southwest adopted FASB Topic 842 as of January 1, 2019. In association with the adoption, the Company recorded adjustments to its Condensed Consolidated Balance Sheet to record right-of-use (“ROU”) assets and lease liabilities of $58.4 million and $60.8 million, respectively. Included in those amounts, Southwest recorded $1.9 million related to both its ROU assets and lease liabilities. Neither the Company nor Southwest experienced a material impact to the Condensed Consolidated Statements of Income from the adoption and no cumulative-effect adjustment to the opening balance of retained earnings was recognized. Management elected to adopt the standard under the optional transition method (refer to Recent Accounting Standards Updates in Note 1 – Background, Organization, and Summary of Significant Accounting Policies), and elected the following Topic 842 practical expedients and accounting policy elections:

•

To use the “package”, which is a set of three practical expedients that must be elected as a package and applied consistently to all of Southwest’s and Centuri’s leases. These include: not reassessing whether any expired or existing contracts are or contain leases; not reassessing the lease classification for expired or existing leases (that is, existing operating and capital leases in accordance with current lease guidance will in each case be classified as operating and finance leases, respectively, under the updated guidance); and not reassessing initial direct costs for any existing leases.


•	To utilize the practical expedient to exclude all easements in place prior to January 1, 2019 from treatment under Topic 842. However, Southwest will evaluate new easements entered into after the effective date of the standard to determine if the arrangements should be accounted for as leases.


•	To make an accounting policy election by asset class to include both the lease and non-lease components (as defined in the guidance) as a single component.


•	To make an accounting policy election to not apply Topic 842 to short-term leases, as permitted.


•	To not elect to use hindsight in determining the lease term and in assessing impairment of ROU assets.


•	To utilize a portfolio approach to effectively account for the operating lease ROU assets and liabilities with regard to certain equipment leases at Centuri.

Southwest and Centuri determine if an arrangement is a lease at inception. ROU assets represent the right to use an underlying asset for the lease term; lease liabilities represent obligations to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. As most of Southwest’s and Centuri’s leases do not provide an implicit interest rate, an incremental borrowing rate based on information available at commencement is used in determining the present value of lease payments; an implicit rate, if readily determinable, is used. Lease terms utilized in the computations may include options to extend or terminate the lease when it is reasonably certain that the option will be exercised.

Southwest’s leases are comprised primarily of operating leases of buildings, land, and equipment. Southwest has no finance leases and no significant short-term leases. Southwest’s leases have a remaining term of 1 to 10 years, some of which include options to extend the lease up to 3 years. Southwest is currently not a lessor in any significant lease arrangements. Southwest’s ROU assets are included in Gas plant, and its lease liabilities are included in, depending upon maturity, Other current liabilities or Other deferred credits and other long-term liabilities on the Company’s and Southwest’s Condensed Consolidated Balance Sheets as of September 30, 2019.

Centuri has operating and finance leases for corporate and field offices, construction equipment, and transportation vehicles. Centuri is currently not a lessor in any significant lease arrangements. Centuri’s leases have remaining lease terms of up to 19 years. Some of these include options to extend the leases, generally for optional terms of up to 5 years, and some include options to terminate the leases within 1 year. Centuri’s equipment leases may include variable payment terms in addition to the fixed lease payments if machinery is used in excess of the standard work periods. These variable payments are not probable of occurring under the current operating environment and have not been included in consideration of lease payments. Short-term leases of Centuri are not accounted for under the provisions of Topic 842, as permitted. Due to the seasonality of Centuri’s business, expense for short-term leases will fluctuate throughout the year with higher expense incurred during the warmer months. As of September 30, 2019 Centuri executed lease agreements that had not yet commenced. These lease agreements primarily relate to real estate leases that have terms ranging from December 2019 through August 2032. Total future lease payments over the lease terms are approximately $13.2 million. Centuri’s ROU assets are included in Other property and investments, and its lease liabilities for operating and finance leases are included, depending upon maturity, in Other current liabilities or Other deferred credits and other long-term liabilities on the Company’s Condensed Consolidated Balance Sheet as of September 30, 2019.

The components of lease expense were as follows:



(Thousands of dollars)	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019
Southwest:
Operating lease cost	$	350	$	1,165

Centuri:
Operating lease cost	$	3,026	$	9,069

Finance lease cost:
Amortization of ROU assets	$	34	$	103
Interest on lease liabilities	10		24
Total finance lease cost	44		127
Short-term lease cost	5,017		10,949
Total lease cost	$	8,437	$	21,310

Supplemental cash flow information related to leases for the nine months ended September 30, 2019 is as follows:



(Thousands of dollars)	Southwest		Centuri		Consolidated Total
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	976	$	8,104	$	9,080
Operating cash flows from finance leases	—		24		24
Financing cash flows from finance leases	—		161		161

ROU assets obtained in exchange for lease obligations:
Operating leases	$	1,143	$	21,653	$	22,796
Finance leases	—		386		386

Supplemental information related to leases, including location in the Condensed Consolidated Balance Sheets, is as follows:



(Thousands of dollars)	September 30, 2019
Southwest:
Operating leases:
Net Utility Plant	$	2,008

Other current liabilities	$	826
Other deferred credits and other long-term liabilities	1,209
Total operating lease liabilities	$	2,035

Weighted average remaining lease term (in years)	3.77
Weighted average discount rate	3.35		%

Centuri:
Operating leases:
Other property and investments	$	71,377

Other current liabilities	8,183
Other deferred credits and other long-term liabilities	65,791
Total operating lease liabilities	$	73,974

Finance leases:
Other property and investments	$	788

Other current liabilities	256
Other deferred credits and other long-term liabilities	400
Total finance lease liabilities	$	656

Weighted average remaining lease term (in years)
Operating leases	9.43
Finance leases	1.79

Weighted average discount rate
Operating leases	4.08		%
Finance leases	5.95		%

The following are schedules of maturities of lease liabilities as of September 30, 2019:



(Thousands of dollars)	Operating leases
Southwest:
2020	$	946
2021	548
2022	244
2023	79
2024	79
Thereafter	267
Total lease payments	2,163
Less imputed interest	128
Total	$	2,035



(Thousands of dollars)	Operating leases		Finance leases
Centuri:
2020	$	11,336	$	289
2021	10,416		174
2022	9,675		165
2023	8,192		95
2024	6,973		3
Thereafter	45,564		—
Total lease payments	92,156		726
Less imputed interest	18,182		70
Total	$	73,974	$	656

As the Company and Southwest adopted Topic 842 using the optional transition method referred to in Note 1 – Background, Organization, and Summary of Significant Accounting Policies, the recent annual disclosure of rental and lease payments as of December 31, 2018 in accordance with Topic 840 is presented in the table below (thousands of dollars):



	2018		2017
Southwest Gas Corporation	$	4,556	$	4,926
Centuri	59,491		62,310
Consolidated rental payments/lease expense	$	64,047	$	67,236

The following is a schedule of future minimum lease payments for operating leases (with initial or remaining terms in excess of one year) as of December 31, 2018 (thousands of dollars):



	Southwest		Centuri		Consolidated Total
2019	$	898	$	10,053	$	10,951
2020	363		7,656		8,019
2021	299		5,760		6,059
2022	163		5,163		5,326
2023	79		3,681		3,760
Thereafter	177		10,511		10,688
Total minimum lease payments	$	1,979	$	42,824	$	44,803

As of December 31, 2018 Centuri leased certain construction equipment under capital leases arrangements which were not significant.

Leases

Note 4 – Leases

•


•	To utilize the practical expedient to exclude all easements in place prior to January 1, 2019 from treatment under Topic 842. However, Southwest will evaluate new easements entered into after the effective date of the standard to determine if the arrangements should be accounted for as leases.


•	To make an accounting policy election by asset class to include both the lease and non-lease components (as defined in the guidance) as a single component.


•	To make an accounting policy election to not apply Topic 842 to short-term leases, as permitted.


•	To not elect to use hindsight in determining the lease term and in assessing impairment of ROU assets.


•	To utilize a portfolio approach to effectively account for the operating lease ROU assets and liabilities with regard to certain equipment leases at Centuri.

The components of lease expense were as follows:



(Thousands of dollars)	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019
Southwest:
Operating lease cost	$	350	$	1,165

Centuri:
Operating lease cost	$	3,026	$	9,069

Finance lease cost:
Amortization of ROU assets	$	34	$	103
Interest on lease liabilities	10		24
Total finance lease cost	44		127
Short-term lease cost	5,017		10,949
Total lease cost	$	8,437	$	21,310

Supplemental cash flow information related to leases for the nine months ended September 30, 2019 is as follows:



(Thousands of dollars)	Southwest		Centuri		Consolidated Total
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	976	$	8,104	$	9,080
Operating cash flows from finance leases	—		24		24
Financing cash flows from finance leases	—		161		161

ROU assets obtained in exchange for lease obligations:
Operating leases	$	1,143	$	21,653	$	22,796
Finance leases	—		386		386

Supplemental information related to leases, including location in the Condensed Consolidated Balance Sheets, is as follows:



(Thousands of dollars)	September 30, 2019
Southwest:
Operating leases:
Net Utility Plant	$	2,008

Other current liabilities	$	826
Other deferred credits and other long-term liabilities	1,209
Total operating lease liabilities	$	2,035

Weighted average remaining lease term (in years)	3.77
Weighted average discount rate	3.35		%

Centuri:
Operating leases:
Other property and investments	$	71,377

Other current liabilities	8,183
Other deferred credits and other long-term liabilities	65,791
Total operating lease liabilities	$	73,974

Finance leases:
Other property and investments	$	788

Other current liabilities	256
Other deferred credits and other long-term liabilities	400
Total finance lease liabilities	$	656

Weighted average remaining lease term (in years)
Operating leases	9.43
Finance leases	1.79

Weighted average discount rate
Operating leases	4.08		%
Finance leases	5.95		%

The following are schedules of maturities of lease liabilities as of September 30, 2019:



(Thousands of dollars)	Operating leases
Southwest:
2020	$	946
2021	548
2022	244
2023	79
2024	79
Thereafter	267
Total lease payments	2,163
Less imputed interest	128
Total	$	2,035



(Thousands of dollars)	Operating leases		Finance leases
Centuri:
2020	$	11,336	$	289
2021	10,416		174
2022	9,675		165
2023	8,192		95
2024	6,973		3
Thereafter	45,564		—
Total lease payments	92,156		726
Less imputed interest	18,182		70
Total	$	73,974	$	656



	2018		2017
Southwest Gas Corporation	$	4,556	$	4,926
Centuri	59,491		62,310
Consolidated rental payments/lease expense	$	64,047	$	67,236

The following is a schedule of future minimum lease payments for operating leases (with initial or remaining terms in excess of one year) as of December 31, 2018 (thousands of dollars):



	Southwest		Centuri		Consolidated Total
2019	$	898	$	10,053	$	10,951
2020	363		7,656		8,019
2021	299		5,760		6,059
2022	163		5,163		5,326
2023	79		3,681		3,760
Thereafter	177		10,511		10,688
Total minimum lease payments	$	1,979	$	42,824	$	44,803

As of December 31, 2018 Centuri leased certain construction equipment under capital leases arrangements which were not significant.

Derivatives

9 Months Ended

Sep. 30, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivatives

Note 5 – Derivatives

In managing its natural gas supply portfolios, Southwest has historically entered into fixed- and variable-price contracts, which qualify as derivatives. Additionally, Southwest has utilized fixed-for-floating swap contracts (“Swaps”) to supplement its fixed-price contracts. The fixed-price contracts, firm commitments to purchase a fixed amount of gas in the future at a fixed price, qualify for the normal purchases and normal sales exception that is allowed for contracts that are probable of delivery in the normal course of business, and are exempt from fair value reporting. The variable-price contracts qualify as derivative instruments; however, because the contract prices are the prevailing prices at the future transaction dates, the contracts have no determinable fair value. The Swap contract prices are determined at the beginning of each month to reflect that month’s published first of month index price and are recorded at fair value. Southwest does not utilize derivative financial instruments for speculative purposes, nor does it have trading operations.

Southwest historically utilized fixed-price contracts and Swaps under its volatility mitigation programs to effectively fix the price on a portion of its natural gas supply portfolios. The maturities of the outstanding Swaps highly correlate to forecasted purchases of natural gas, with the longest maturity date of the Swaps being October 2020. Management does not currently anticipate entering into new Swaps in the near term. Regarding existing Swap arrangements, Southwest pays the counterparty a fixed rate and receives from the counterparty a floating rate per MMBtu (“dekatherm”) of natural gas. Only the net differential is paid or received. The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms):



	September 30, 2019	December 31, 2018
Contract notional amounts	16,071	13,387

The following table shows the amounts Southwest paid to and received from counterparties for settlements of matured Swaps:



(Thousands of dollars)	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019		Twelve Months Ended September 30, 2019
Paid to counterparties	$	2,191	$	8,338	$	10,322
Received from counterparties	$	10	$	1,057	$	1,657

Pursuant to regulatory deferral accounting treatment for rate-regulated entities, unrealized gains and losses in fair value of the Swaps are recorded as a regulatory asset and/or liability. When the Swaps mature, any prior positions held are reversed and the settled position is recorded as an increase or decrease of purchased gas under the related purchase gas adjustment (“PGA”) mechanism in determining the deferred PGA balances. Neither changes in fair value nor settled amounts of Swaps have a direct effect on earnings or other comprehensive income, since following settlement, amounts are reflected in Net cost of gas sold at the same time they are included in Gas operating revenues through updates to the PGA component of rates.

Previously, Southwest entered into forward-starting interest rate swaps (“FSIRS”), the settled positions for which are immaterial and continue to be amortized from Accumulated other comprehensive income (loss) into interest expense.

The estimated fair value of Southwest’s Swaps were determined at September 30, 2019 and December 31, 2018 using futures settlement prices for the delivery of natural gas at Henry Hub adjusted by the price of future settlement bases, which reflect the difference between the price of natural gas at a given delivery basin and the Henry Hub pricing points. These Level 2 inputs are observable in the marketplace throughout the full term of the Swaps and have been credit-risk adjusted with no significant impact to the overall fair value measurement. The following table sets forth the fair value of the Swaps and their location in the Condensed Consolidated Balance Sheets for both the Company and Southwest (thousands of dollars). It also sets forth the location of regulatory assets or liabilities offsetting, dollar-for-dollar, the fair value of the Swaps (pursuant to Southwest’s rate-regulation):

Fair values of derivatives not designated as hedging instruments:



September 30, 2019
Swap Position
Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total			Offsetting Balance Sheet Location (Regulatory Asset/(Liability))
Swaps	Deferred charges and other assets	$	48	$	(27	)	$	21		Other deferred credits
Swaps	Other current liabilities	103		(9,837		)	(9,734		)	Prepaid and other current assets
Swaps	Other deferred credits	—		(335		)	(335		)	Deferred charges and other assets
Total		$	151	$	(10,199	)	$	(10,048	)

December 31, 2018
Swap Position
Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total			Offsetting Balance Sheet Location (Regulatory Asset/(Liability))
Swaps	Prepaid and other current assets	$	243	$	(99	)	$	144		Other current liabilities
Swaps	Other current liabilities	1,595		(3,347		)	(1,752		)	Prepaid and other current assets
Swaps	Other deferred credits	141		(251		)	(110		)	Deferred charges and other assets
Total		$	1,979	$	(3,697	)	$	(1,718	)

Master netting arrangements exist with each counterparty that provide for the net settlement (in the settlement month) of all contracts through a single payment. As applicable, management has elected to reflect the net amounts in its balance sheets. There was no outstanding collateral associated with the Swaps during either period shown in the above table.

Common Stock

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

Common Stock

Note 6 – Common Stock

Only shares of the Company’s common stock are publicly traded on the New York Stock Exchange, under the ticker symbol “SWX.” Share-based compensation related to Southwest and Centuri is based on stock awards to be issued in shares of Southwest Gas Holdings, Inc.

On May 8, 2019, the Company filed with the SEC an automatic shelf registration statement on Form S-3 (File No. 333-231297), which became effective upon filing, for the offer and sale of up to $300 million of common stock from time to time in at-the-market offerings under the prospectus included therein and in accordance with the Sales Agency Agreement, dated May 8, 2019, between the Company and BNY Mellon Capital Markets, LLC (the “Equity Shelf Program”). The following table provides the activity under the Equity Shelf Program for the quarter and life-to-date ended September 30, 2019:



	Three Months Ended			Life-To-Date Ended
	September 30,
	2019			2019
Gross proceeds	$	24,337,600		$	99,337,371
Less: agent commissions	(243,375		)	(993,373		)
Net proceeds	$	24,094,225		$	98,343,998

Number of shares sold	273,594			1,146,955
Weighted average price per share	$	88.96		$	86.61

As of September 30, 2019, the Company had up to $200,662,629 of common stock available for sale under the program. Net proceeds from the sales of shares of common stock under the Equity Shelf Program are intended for general corporate purposes, including the acquisition of property for the construction, completion, extension or improvement of pipeline systems and facilities located in and around the communities served by Southwest. Net proceeds during the nine months ended September 30, 2019 were contributed to, and reflected in the records of, Southwest (as a capital contribution from Southwest Gas Holdings, Inc.).

During the quarter ended March 31, 2019, the Company sold approximately 278,000 shares of common stock under a previously effective equity shelf program. Those issuances reflected the remaining shares available under that previous program.

During the nine months ended September 30, 2019, the Company issued approximately 76,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Also during the nine months ended September 30, 2019, the Company issued 96,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan (“DRSPP”), raising approximately $8.1 million.

On September 20, 2019, coincident with the reincorporation into Delaware, the Company increased the number of authorized shares of common stock available for issuance from 60,000,000 to 120,000,000.

Long-Term Debt

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Long-Term Debt

Note 7 – Long-Term Debt

Long-term debt is recognized in the Company’s and Southwest’s Condensed Consolidated Balance Sheets generally at the carrying value of the obligations outstanding. However, details surrounding the fair value and individual carrying values of instruments are discussed below or provided in the table that follows.

Southwest’s revolving credit facility (including commercial paper) and the variable-rate Industrial Development Revenue Bonds (“IDRBs”) approximate their carrying values. The revolving credit facility and IDRBs are categorized as Level 1 due to Southwest’s ability to access similar debt arrangements at measurement dates with comparable terms, including variable/market rates. Additionally, the revolving credit facility is generally repaid quickly and the IDRBs have interest rates that reset frequently.

The fair values of Southwest’s debentures (which include senior and medium-term notes) were determined utilizing a market-based valuation approach, where fair values are determined based on evaluated pricing data, such as broker quotes and yields for similar securities adjusted for observable differences. Significant inputs used in the valuation generally include benchmark yield curves, credit ratings, and issuer spreads. The external credit rating, coupon rate, and maturity of each security are considered in the valuation, as applicable. The fair values of debentures are categorized as Level 2.

The Centuri secured revolving credit and term loan facility and Centuri’s other debt obligations (not actively traded) are categorized as Level 3. Because Centuri’s debt is not publicly traded, fair values for the secured revolving credit and term loan facility and its other debt obligations were based on a conventional discounted cash flow methodology and utilizing current market pricing yield curves, across Centuri’s debt maturity spectrum, of other industrial bonds with an assumed credit rating comparable to the Company’s.



	September 30, 2019					December 31, 2018
	Carrying Amount			Market Value		Carrying Amount			Market Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 4.45%, due 2020	$	125,000		$	126,763	$	125,000		$	126,213
Notes, 6.1%, due 2041	125,000			167,619		125,000			150,728
Notes, 3.875%, due 2022	250,000			257,930		250,000			254,195
Notes, 4.875%, due 2043	250,000			303,955		250,000			268,985
Notes, 3.8%, due 2046	300,000			316,383		300,000			267,030
Notes, 3.7%, due 2028	300,000			323,034		300,000			298,926
Notes, 4.15%, due 2049	300,000			334,680		—			—
8% Series, due 2026	75,000			97,769		75,000			93,827
Medium-term notes, 7.78% series, due 2022	25,000			27,655		25,000			27,497
Medium-term notes, 7.92% series, due 2027	25,000			32,250		25,000			30,016
Medium-term notes, 6.76% series, due 2027	7,500			9,218		7,500			8,651
Unamortized discount and debt issuance costs	(14,852		)			(11,807		)
	1,767,648					1,470,693
Revolving credit facility and commercial paper	150,000			150,000		150,000			150,000
Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028	50,000			50,000		50,000			50,000
2003 Series A, due 2038	50,000			50,000		50,000			50,000
2008 Series A, due 2038	50,000			50,000		50,000			50,000
2009 Series A, due 2039	50,000			50,000		50,000			50,000
Unamortized discount and debt issuance costs	(1,778		)			(2,024		)
	198,222					197,976
Less: current maturities	—					—
Long-term debt, less current maturities - Southwest Gas Corporation	$	2,115,870				$	1,818,669
Centuri:
Centuri term loan facility	$	248,043		$	257,475	$	255,959		$	260,135
Unamortized debt issuance costs	(1,171		)			(1,414		)
	246,872					254,545
Centuri secured revolving credit facility	89,140			89,175		—			—
Centuri other debt obligations	48,399			49,393		67,104			67,053
Less: current maturities	(38,165		)			(33,060		)
Long-term debt, less current maturities - Centuri	$	346,246				$	288,589
Consolidated Southwest Gas Holdings, Inc.:
Southwest Gas Corporation long-term debt	$	2,115,870				$	1,818,669
Centuri long-term debt	384,411					321,649
Less: current maturities	(38,165		)			(33,060		)
Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	2,462,116				$	2,107,258

Southwest has a $400 million credit facility that is scheduled to expire in March 2022. Southwest designates $150 million of capacity related to the facility as long-term debt and has designated the remaining $250 million for working capital purposes. Interest rates for the credit facility are calculated at either the London Interbank Offered Rate (“LIBOR”) or an “alternate base rate,” plus in each case an applicable margin that is determined based on Southwest’s senior unsecured debt rating. At September 30, 2019, the applicable margin is 1% for loans bearing interest with reference to LIBOR and 0% for loans bearing interest with reference to the alternative base rate. At September 30, 2019, $150 million was outstanding on the long-term portion (including $50 million under the commercial paper program, discussed below) and $30 million of borrowings were outstanding on the short-term portion of this credit facility (see Note 8 – Short-Term Debt).

Southwest has a $50 million commercial paper program. Any issuance under the commercial paper program is supported by Southwest’s current revolving credit facility and, therefore, does not represent additional borrowing capacity under the credit facility. Borrowings under the commercial paper program are designated as long-term debt. Interest rates for the program are calculated at the then current commercial paper rate. At September 30, 2019, as noted above, $50 million of borrowings were outstanding under the commercial paper program.

In May 2019, Southwest issued $300 million in 4.15% Senior Notes at a discount of 0.051%. The notes will mature in June 2049. The net proceeds were used to repay a portion of amounts then outstanding under its credit facility and commercial paper program.

In November 2018, Centuri, in association with the acquisition of Linetec, amended and restated its senior secured revolving credit and term loan facility, increasing the capacity from $450 million to $590 million; the amended facility is scheduled to expire in November 2023. This facility includes a revolving credit facility and a term loan facility. The line of credit portion of the facility is $325 million; amounts borrowed and repaid under the revolving line of credit facility are available to be re-borrowed. The term loan facility portion has a limit of approximately $265 million. The $590 million revolving credit and term loan facility is secured by substantially all of Centuri’s assets except those explicitly excluded under the terms of the agreement (including owned real estate and certain certificated vehicles). Centuri’s assets securing the facility at September 30, 2019 totaled $1.3 billion. At September 30, 2019, $337 million in borrowings were outstanding under the Centuri facility.

It is currently anticipated that LIBOR may be discontinued as a benchmark or reference rate after 2021. As of September 30, 2019, no borrowings were outstanding for the holding company under its credit facility (see Note 8 – Short-Term Debt), and therefore, there was no related indebtedness with reference to LIBOR. However, $130 million of Southwest’s outstanding borrowings under its credit facility (other than from its commercial paper program) and $218 million of Centuri’s outstanding borrowings under its credit facility have interest rates with reference to LIBOR and maturity dates that extend beyond 2021. Southwest’s outstanding LIBOR referenced debt of $130 million is approximately 6% of Southwest’s total debt, and Southwest’s and Centuri’s combined outstanding LIBOR referenced debt of $348 million is approximately 14% of total debt (including current maturities) for the Company overall. In order to mitigate the impact of the discontinuation on the Company’s financial condition and results of operations, Southwest and Centuri will continue to monitor developments with respect to alternative rates and work with lenders to determine the appropriate alternative reference rate for variable rate indebtedness.

Short-Term Debt	9 Months Ended
Short-Term Debt	Sep. 30, 2019
Debt Disclosure [Abstract]
Short-Term Debt	Note 8 – Short-Term Debt Southwest Gas Holdings, Inc. has a $100 million credit facility that is scheduled to expire in March 2022. There were no borrowings outstanding under this credit facility at September 30, 2019. As discussed in Note 7 – Long-Term Debt, Southwest has a $400 million credit facility that is scheduled to expire in March 2022, of which $250 million has been designated by management for working capital purposes. Southwest had $30 million of short-term borrowings outstanding at September 30, 2019 under this facility.

Other Comprehensive Income and Accumulated Other Comprehensive Income

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

Other Comprehensive Income and Accumulated Other Comprehensive Income

Note 9 – Other Comprehensive Income and Accumulated Other Comprehensive Income

The following information provides insight into amounts impacting the Company’s Other comprehensive income (loss), both before and after-tax impacts, within the Condensed Consolidated Statements of Comprehensive Income, which also impact Accumulated other comprehensive income (“AOCI”) in the Condensed Consolidated Balance Sheets and the Condensed Consolidated Statements of Equity. See Note 5 – Derivatives for additional information on the FSIRS.

Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss)

(Thousands of dollars)



	Three Months Ended September 30, 2019									Three Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Amortization of prior service cost	$	318		$	(77	)	$	241		$	334		$	(80	)	$	254
Amortization of net actuarial (gain)/loss	5,844			(1,402		)	4,442			8,404			(2,017		)	6,387
Regulatory adjustment	(5,348		)	1,283			(4,065		)	(7,560		)	1,814			(5,746		)
Pension plans other comprehensive income	814			(196		)	618			1,178			(283		)	895
FSIRS (designated hedging activities):
Amounts reclassified into net income	836			(201		)	635			836			(200		)	636
FSIRS other comprehensive income	836			(201		)	635			836			(200		)	636
Total other comprehensive income - Southwest Gas Corporation	1,650			(397		)	1,253			2,014			(483		)	1,531
Foreign currency translation adjustments:
Translation adjustments	(447		)	—			(447		)	599			—			599
Foreign currency other comprehensive income (loss)	(447		)	—			(447		)	599			—			599
Total other comprehensive income - Southwest Gas Holdings, Inc.	$	1,203		$	(397	)	$	806		$	2,613		$	(483	)	$	2,130

	Nine Months Ended September 30, 2019									Nine Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Amortization of prior service cost	$	953		$	(229	)	$	724		$	1,002		$	(240	)	$	762
Amortization of net actuarial (gain)/loss	17,532			(4,207		)	13,325			25,212			(6,051		)	19,161
Regulatory adjustment	(16,043		)	3,850			(12,193		)	(22,679		)	5,443			(17,236		)
Pension plans other comprehensive income	2,442			(586		)	1,856			3,535			(848		)	2,687
FSIRS (designated hedging activities):
Amounts reclassified into net income	2,508			(602		)	1,906			2,509			(602		)	1,907
FSIRS other comprehensive income	2,508			(602		)	1,906			2,509			(602		)	1,907
Total other comprehensive income - Southwest Gas Corporation	4,950			(1,188		)	3,762			6,044			(1,450		)	4,594
Foreign currency translation adjustments:
Translation adjustments	1,131			—			1,131			(1,002		)	—			(1,002		)
Foreign currency other comprehensive income (loss)	1,131			—			1,131			(1,002		)	—			(1,002		)
Total other comprehensive income - Southwest Gas Holdings, Inc.	$	6,081		$	(1,188	)	$	4,893		$	5,042		$	(1,450	)	$	3,592



	Twelve Months Ended September 30, 2019									Twelve Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Net actuarial gain/(loss)	$	(20,426	)	$	4,902		$	(15,524	)	$	(43,027	)	$	10,326		$	(32,701	)
Amortization of prior service cost	1,286			(309		)	977			1,336			(367		)	969
Amortization of net actuarial (gain)/loss	25,937			(6,224		)	19,713			31,573			(8,468		)	23,105
Regulatory adjustment	(1,597		)	383			(1,214		)	6,865			(844		)	6,021
Pension plans other comprehensive income (loss)	5,200			(1,248		)	3,952			(3,253		)	647			(2,606		)
FSIRS (designated hedging activities):
Amounts reclassified into net income	3,344			(804		)	2,540			3,346			(920		)	2,426
FSIRS other comprehensive income	3,344			(804		)	2,540			3,346			(920		)	2,426
Total other comprehensive income (loss) - Southwest Gas Corporation	8,544			(2,052		)	6,492			93			(273		)	(180		)
Foreign currency translation adjustments:
Translation adjustments	(877		)	—			(877		)	(1,092		)	—			(1,092		)
Foreign currency other comprehensive income (loss)	(877		)	—			(877		)	(1,092		)	—			(1,092		)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	7,667		$	(2,052	)	$	5,615		$	(999	)	$	(273	)	$	(1,272	)

(1)

Tax amounts are calculated using a 24% rate following the December 22, 2017 enactment date of U.S. tax reform. For periods prior to the enactment date (and included in specific line items of the tables for the twelve months ended September 30, 2018), tax amounts were calculated using a 38% rate. The tax effect of before-tax amounts remaining in the balance of Accumulated other comprehensive income (loss) as of September 30, 2019 is computed using a 24% tax rate overall. With regard to foreign currency translation adjustments, the Company has elected to indefinitely reinvest the earnings of Centuri’s Canadian subsidiaries in Canada, thus preventing deferred taxes on such earnings. As a result of this assertion, and no repatriation of earnings anticipated, the Company is not recognizing a tax effect or presenting a tax expense or benefit for currency translation adjustments reported in Other comprehensive income (loss).

Approximately $2.5 million of realized losses (net of tax) related to the FSIRS, reported in Accumulated other comprehensive income (loss) at September 30, 2019, will be reclassified into interest expense within the next 12 months as the related interest payments on long-term debt occur.

The following table represents a rollforward of AOCI, presented on the Company’s Condensed Consolidated Balance Sheets (thousands of dollars):



	Defined Benefit Plans									FSIRS									Foreign Currency Items
	Before-Tax			Tax (Expense) Benefit (4,5)			After-Tax (5)			Before-Tax			Tax (Expense) Benefit (4,5)			After-Tax (5)			Before-Tax			Tax (Expense) Benefit		After-Tax			AOCI
Beginning Balance AOCI December 31, 2018	$	(55,227	)	$	13,254		$	(41,973	)	$	(9,310	)	$	2,234		$	(7,076	)	$	(3,619	)	$	—	$	(3,619	)	$	(52,668	)
Translation adjustments	—			—			—			—			—			—			1,131			—		1,131			1,131
Other comprehensive income (loss) before reclassifications	—			—			—			—			—			—			1,131			—		1,131			1,131
FSIRS amounts reclassified from AOCI (1)	—			—			—			2,508			(602		)	1,906						—		—			1,906
Amortization of prior service cost (2)	953			(229		)	724			—			—			—			—			—		—			724
Amortization of net actuarial loss (2)	17,532			(4,207		)	13,325			—			—			—			—			—		—			13,325
Regulatory adjustment (3)	(16,043		)	3,850			(12,193		)	—			—			—			—			—		—			(12,193		)
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	2,442			(586		)	1,856			2,508			(602		)	1,906			1,131			—		1,131			4,893
Ending Balance AOCI September 30, 2019	$	(52,785	)	$	12,668		$	(40,117	)	$	(6,802	)	$	1,632		$	(5,170	)	$	(2,488	)	$	—	$	(2,488	)	$	(47,775	)


(1)	The FSIRS reclassification amounts are included in Net interest deductions on the Company’s Condensed Consolidated Statements of Income.


(2)	These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost for additional details).


(3)	The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in Deferred charges and other assets on the Company’s Condensed Consolidated Balance Sheets).


(4)	Tax amounts are calculated using a 24% rate.


(5)	The beginning balances depict amounts attributable to the individual components of AOCI (Defined Benefit Plans and FSIRS) following the adoption of ASU No. 2018-02, with no impact to the total balance of AOCI resulting from the depiction.

The following table represents a rollforward of AOCI, presented on Southwest’s Condensed Consolidated Balance Sheets (thousands of dollars):



	Defined Benefit Plans									FSIRS
	Before-Tax			Tax (Expense) Benefit (9,10)			After-Tax (10)			Before-Tax			Tax (Expense) Benefit (9,10)			After-Tax (10)			AOCI
Beginning Balance AOCI December 31, 2018	$	(55,227	)	$	13,254		$	(41,973	)	$	(9,310	)	$	2,234		$	(7,076	)	$	(49,049	)
FSIRS amounts reclassified from AOCI (6)	—			—			—			2,508			(602		)	1,906			1,906
Amortization of prior service cost (7)	953			(229		)	724			—			—			—			724
Amortization of net actuarial loss (7)	17,532			(4,207		)	13,325			—			—			—			13,325
Regulatory adjustment (8)	(16,043		)	3,850			(12,193		)	—			—			—			(12,193		)
Net current period other comprehensive income attributable to Southwest Gas Corporation	2,442			(586		)	1,856			2,508			(602		)	1,906			3,762
Ending Balance AOCI September 30, 2019	$	(52,785	)	$	12,668		$	(40,117	)	$	(6,802	)	$	1,632		$	(5,170	)	$	(45,287	)


(6)	The FSIRS reclassification amounts are included in Net interest deductions on Southwest’s Condensed Consolidated Statements of Income.


(7)	These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost for additional details).


(8)	The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in Deferred charges and other assets on Southwest’s Condensed Consolidated Balance Sheets).


(9)	Tax amounts are calculated using a 24% rate.


(10)	The beginning balances depict amounts attributable to the individual components of AOCI (Defined Benefit Plans and FSIRS) following the adoption of ASU No. 2018-02, with no impact to the total balance of AOCI resulting from the depiction.

The following table represents amounts (before income tax impacts) included in AOCI (in the tables above), that have not yet been recognized in net periodic benefit cost (thousands of dollars):



	September 30, 2019			December 31, 2018
Net actuarial (loss) gain	$	(417,832	)	$	(435,364	)
Prior service cost	(2,080		)	(3,033		)
Less: amount recognized in regulatory assets	367,127			383,170
Recognized in AOCI	$	(52,785	)	$	(55,227	)

Segment Information

9 Months Ended

Sep. 30, 2019

Segment Reporting [Abstract]

Segment Information

Note 10 – Segment Information

The Company has two reportable segments: natural gas operations and utility infrastructure services. Southwest has a single reportable segment that is referred to herein as the natural gas operations segment of the Company. In order to reconcile to net income as disclosed in the Condensed Consolidated Statements of Income, an Other column is included associated with impacts of corporate and administrative activities related to Southwest Gas Holdings, Inc. The following tables present revenues from external customers, intersegment revenues, and segment net income for the two reportable segments (thousands of dollars):



	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Three Months Ended September 30, 2019
Revenues from external customers	$	209,980		$	480,896	$	—		$	690,876
Intersegment revenues	—			34,354		—			34,354
Total	$	209,980		$	515,250	$	—		$	725,230
Segment net income (loss)	$	(20,012	)	$	25,838	$	(473	)	$	5,353

Three Months Ended September 30, 2018
Revenues from external customers	$	217,523		$	414,175	$	—		$	631,698
Intersegment revenues	—			36,448		—			36,448
Total	$	217,523		$	450,623	$	—		$	668,146
Segment net income (loss)	$	(13,670	)	$	26,798	$	(797	)	$	12,331

	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Nine Months Ended September 30, 2019
Revenues from external customers	$	989,368		$	1,160,303	$	—		$	2,149,671
Intersegment revenues	—			122,109		—			122,109
Total	$	989,368		$	1,282,412	$	—		$	2,271,780
Segment net income (loss)	$	86,746		$	36,725	$	(1,253	)	$	122,218

Nine Months Ended September 30, 2018
Revenues from external customers	$	987,515		$	1,009,166	$	—		$	1,996,681
Intersegment revenues	—			96,678		—			96,678
Total	$	987,515		$	1,105,844	$	—		$	2,093,359
Segment net income (loss)	$	79,301		$	35,034	$	(1,362	)	$	112,973

	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Twelve Months Ended September 30, 2019
Revenues from external customers	$	1,359,581		$	1,537,508	$	—		$	2,897,089
Intersegment revenues	—			161,345		—			161,345
Total	$	1,359,581		$	1,698,853	$	—		$	3,058,434
Segment net income (loss)	$	146,287		$	46,668	$	(1,433	)	$	191,522

Twelve Months Ended September 30, 2018
Revenues from external customers	$	1,354,000		$	1,358,418	$	—		$	2,712,418
Intersegment revenues	—			121,374		—			121,374
Total	$	1,354,000		$	1,479,792	$	—		$	2,833,792
Segment net income (loss)	$	153,683		$	57,677	$	(1,922	)	$	209,438

Redeemable Noncontrolling Interests

9 Months Ended

Sep. 30, 2019

Noncontrolling Interest [Abstract]

Redeemable Noncontrolling Interests

Note 11 – Redeemable Noncontrolling Interest

In connection with the acquisition of Linetec in November 2018, the previous owner retained a 20% equity interest in Linetec, the reduction of which is subject to certain rights based on the passage of time or upon the occurrence of certain triggering events. Effective January 2022, the Company has the right, but not the obligation, to purchase at fair value (subject to a floor) a portion of the interest held by the noncontrolling party, and in incremental amounts each year thereafter. The shares subject to the election accumulate (if earlier elections are not made) such that 100% of the interest retained by the noncontrolling party is subject to the election beginning in 2024. If the Company does not exercise its rights at each or any of the specified intervals, the noncontrolling party has the ability, but not the obligation, to exit their investment retained by requiring the Company to purchase a similar portion of their interest up to the maximum cumulative amounts specified at each interval discussed above. The Company has determined that this noncontrolling interest is a redeemable noncontrolling interest and, in accordance with SEC guidance, is classified as mezzanine equity (temporary equity) in the Company’s Condensed Consolidated Balance Sheets.

Significant changes in the value of the redeemable noncontrolling interest, above a floor established at the acquisition date, are recognized as they occur, and the carrying value is adjusted as necessary at each reporting date. The fair value is estimated using a market approach that utilizes certain financial metrics from guideline public companies of similar industry and operating characteristics. However, the carrying value of the redeemable noncontrolling interest was greater than its fair value as of September 30, 2019, and no previous upward redemption value adjustments were made following the acquisition date. SEC guidance indicates that a redemption value adjustment would not be made under these circumstances. The following depicts the change to the balance of the redeemable noncontrolling interest:



(Thousands of dollars):	Redeemable Noncontrolling Interest
Balance, December 31, 2018	$	81,831
Net income attributable to redeemable noncontrolling interest	2,523
Balance, September 30, 2019	$	84,354

Business Acquisitions

9 Months Ended

Sep. 30, 2019

Business Combinations [Abstract]

Business Acquisitions

Note 12 – Business Acquisitions

In November 2018, the Company, through its subsidiaries, led principally by Centuri, completed the acquisition of an 80% interest in a privately held infrastructure services business, Linetec, with the remaining 20% retained by the seller. See the Company’s 2018 Form 10-K for additional information about this acquisition.

Assets acquired and liabilities assumed in the transaction were recorded, generally, at their estimated acquisition date fair values. During the measurement period, which may be up to one year from the acquisition date, the Company may continue to record adjustments to the fair value of tangible and intangible assets acquired and liabilities assumed. The Company continues to collect information and reevaluates these estimates and assumptions quarterly. Upon the conclusion of the measurement period or final determination of the fair value of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments may be recognized in the Company’s Consolidated Statement of Income.

The Company’s allocation of the purchase price was based on an evaluation of the appropriate fair values and represented management’s best estimate based on available data (including market data, data regarding customers of the acquired business, terms of acquisition-related agreements, analysis of historical and projected results, and other types of data). The analysis included consideration of types of intangibles that were acquired, including customer relationships, trade names, and customer contracts. Certain payments were estimated as of the acquisition date and are adjusted when paid or as estimates change based on available data; the final purchase accounting has not yet been completed. Further adjustments may occur, including potential changes to final purchase consideration payments held back, such as the remaining amounts associated with unbilled customer accounts receivable balances recorded at their estimated realizable values as of the acquisition date. Subsequent to the acquisition date and through September 30, 2019, Centuri recorded a net reduction to the overall purchase price of $25.2 million related to the combined effects of a mutual tax election under Internal Revenue Code Section 338(h)(10), working capital adjustments, amounts associated with certain unbilled customer receivable balances, and other refinements to the valuation, which impacted the remaining unremitted consideration. Approximately $19.5 million of previously unremitted consideration was paid during the nine months ending September 30, 2019. As of that date, remaining unpaid consideration was $26.2 million.

The preliminary estimated fair values of assets acquired and liabilities assumed as of November 30, 2018, are as follows (millions of dollars):



	Acquisition Date		Measurement Period Adjustments			Revised Acquisition Date
Cash and cash equivalents	$	3.9	$	—		$	3.9
Accounts receivable	32.8		(0.5		)	32.3
Revenue earned on contracts in progress in excess of billings	21.6		(0.2		)	21.4
Prepaid expenses and other current assets	1.1		0.1			1.2
Property and equipment	89.4		(0.8		)	88.6
Intangible assets	89.3		—			89.3
Goodwill	188.5		(22.2		)	166.3
Total assets acquired	426.6		(23.6		)	403.0

Accounts payable	8.0		—			8.0
Accrued liabilities	6.9		1.6			8.5
Deferred compensation and related accrued taxes	3.4		—			3.4
Redeemable noncontrolling interest	81.7		—			81.7
Total liabilities assumed and noncontrolling interest	100.0		1.6			101.6
Net assets acquired	$	326.6	$	(25.2	)	$	301.4

The Company incurred and expensed acquisition costs of $6.9 million which are included in Utility infrastructure services expenses on the Company’s Consolidated Statement of Income for the year ended December 31, 2018. No acquisition-related costs were incurred during the three and nine months ended September 30, 2019, and no significant impacts to earnings resulted from the measurement-period adjustments reflected above.

The preliminary allocation of the purchase price of Linetec was accounted for in accordance with applicable accounting guidance. Goodwill consists of the value associated with the assembled workforce, consolidation of operations, and the estimated economic value attributable to future opportunities related to the transaction. As the business of Linetec was deemed an asset purchase for tax purposes, the tax-basis goodwill is expected to be deductible for tax purposes. During 2019, values at the acquisition date were adjusted, as reflected in the table above, on the Company’s Condensed Consolidated Balance Sheets.

Background, Organization, and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations. Southwest Gas Holdings, Inc. is a holding company, owning all of the shares of common stock of Southwest Gas Corporation (“Southwest” or the “natural gas operations” segment) and all of the shares of common stock of Centuri Group, Inc. (“Centuri,” or the “utility infrastructure services” segment). At the annual meeting of shareholders of Southwest Gas Holdings, Inc., held on May 2, 2019, shareholders voted to approve changing the state of incorporation for Southwest Gas Holdings, Inc. from California to Delaware. The reincorporation became effective September 20, 2019. Southwest is engaged in the business of purchasing, distributing, and transporting natural gas for customers in portions of Arizona, Nevada, and California. Public utility rates, practices, facilities, and service territories of Southwest are subject to regulatory oversight. The timing and amount of rate relief can materially impact results of operations. Natural gas purchases and the timing of related recoveries can materially impact liquidity. Results for the natural gas operations segment are higher during winter periods due to the seasonality incorporated in its regulatory rate structures. Centuri is a comprehensive utility infrastructure services enterprise dedicated to delivering a diverse array of solutions to North America’s gas and electric providers. Centuri derives revenue from installation, replacement, repair, and maintenance of energy distribution systems, and developing industrial construction solutions. Centuri operations are generally conducted under the business names of NPL Construction Co. (“NPL”), NPL Canada Ltd. (“NPL Canada”), New England Utility Constructors, Inc. (“Neuco”), and Linetec Services, LLC (“Linetec”). Utility infrastructure services activity is seasonal in most of Centuri’s operating areas. Peak periods are the summer and fall months in colder climate areas, such as the northeastern and midwestern United States (“U.S.”) and in Canada. In warmer climate areas, such as the southwestern and southeastern U.S., utility infrastructure services activity continues year round. In November 2017, Centuri acquired Neuco, thereby expanding its core services in the northeast region of the U.S. Additionally, in November 2018, Centuri expanded its operations in the southeast region of the U.S. through the acquisition of an 80% interest in Linetec. See Note 12 – Business Acquisitions for more information.
Basis of Presentation	Basis of Presentation. The condensed consolidated financial statements of Southwest Gas Holdings, Inc. and subsidiaries (the “Company”) and Southwest included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The year-end condensed balance sheet data was derived from audited financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) have been condensed or omitted pursuant to such rules and regulations. No substantive change has occurred with regard to the Company’s business segments on the whole, or in the primary businesses comprising those segments as a result of the foregoing acquisitions of Neuco and Linetec. The preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of management, all adjustments, consisting of normal recurring items and estimates necessary for a fair depiction of results for the interim periods, have been made. It is suggested that these condensed consolidated financial statements be read in conjunction with the consolidated financial statements and the notes thereto included in the 2018 Annual Report to Shareholders, which is incorporated by reference into the 2018 Form 10-K.
Fair Value Measurements	Fair Value Measurements. Certain assets and liabilities are reported at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. U.S. GAAP states that a fair value measurement should be based on the assumptions that market participants would use in pricing the asset or liability and establishes a fair value hierarchy that ranks the inputs used to measure fair value by their reliability. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to fair values derived from unobservable inputs (Level 3 measurements). Financial assets and liabilities are categorized in their entirety based on the lowest level of input that is significant to the fair value measurement. The three levels of the fair value hierarchy are as follows: Level 1 – quoted prices (unadjusted) in active markets for identical assets or liabilities that a company has the ability to access at the measurement date. Level 2 – inputs other than quoted prices included within Level 1 that are observable for similar assets or liabilities, either directly or indirectly. Level 3 – unobservable inputs for the asset or liability. Unobservable inputs are used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date. The Company primarily used quoted market prices and other observable market pricing information in valuing cash and cash equivalents, derivatives, long-term debt outstanding, and assets of the qualified pension plan and postretirement benefit plans required to be recorded and/or disclosed at fair value.
Cash and Cash Equivalents	Cash and Cash Equivalents. For purposes of reporting consolidated cash flows, cash and cash equivalents include cash on hand and financial instruments with original maturities of three months or less. Such investments are carried at cost, which approximates market value. Cash and cash equivalents for Southwest and the Company also include money market fund investments totaling approximately $1.5 million and $10.2 million, respectively, at September 30, 2019, and $18 million and $59.9 million, respectively, at December 31, 2018, which fall within Level 2 of the fair value hierarchy, due to the asset valuation methods used by money market funds. Typical non-cash investing activities for Southwest include customer advances applied as contributions toward utility construction activity and capital expenditures that were not paid as of quarter end that are included in accounts payable. Amounts related to such activities were immaterial for the periods presented herein. Non-cash investing activities for the twelve months ended September 30, 2019 included $26.2 million of purchase consideration related to the Linetec acquisition by Centuri, in the form of liabilities incurred that remained unpaid as of September 30, 2019; such amounts are included in Other current liabilities on the Condensed Consolidated Balance Sheets of the Company.
Income Taxes	Income Taxes. In 2017, the Tax Cuts and Jobs Act (the “TCJA”) was enacted. The TCJA had significant impacts on the taxation of business entities, including specific provisions related to regulated public utilities. The more significant changes that impacted the Company and Southwest include the reduction in the corporate federal income tax rate from 35% to 21%, and limiting the utilization of net operating losses (“NOLs”) to 80% of taxable income, with the ability to indefinitely carryforward unutilized NOLs to reduce future taxable income.
Goodwill	Goodwill. Goodwill is assessed as of October 1st each year for impairment, or more frequently, if circumstances indicate an impairment to the carrying value of goodwill may have occurred. Management of the Company and Southwest considered its reporting units and segments and determined that its segments and reporting units remain consistent between periods presented below, and that no change was necessary with regard to the level at which goodwill is assessed for impairment.
Recent Accounting Standards Updates	Recent Accounting Standards Updates. Accounting pronouncements adopted in 2019: In February 2016, the Financial Accounting Standards Board (“FASB”) issued the update “Leases (Topic 842).” Under the update, lessees were required to recognize a lease liability for the obligation to make lease payments, measured on a discounted basis; and a right-of-use asset for the right to use, or control the use of, a specified asset for the lease term. The Company and Southwest adopted Topic 842 in the first quarter of 2019 through an optional transition method, which was elected, permitting the application of the provisions of the standard at the adoption date, rather than to earlier comparative periods. As a result, the Company and Southwest have not recast prior periods to reflect the adoption of this standard. See Note 4 – Leases. Accounting pronouncements that will be effective after 2019: In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13 update “Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The update requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The inputs currently used to estimate credit losses will still be used; however, they may be adapted to reflect the full amount of expected losses. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. All entities may adopt the amendments in this update earlier as of fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Management is evaluating what impact, if any, this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures. In January 2017, the FASB issued ASU 2017-04 “Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” Under the update, an entity will apply a one-step quantitative test as opposed to a two-step test as currently required, and record the amount of goodwill impairment as the excess of a reporting unit's carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment. The amount of any goodwill impairment calculated under the update could vary from the calculation under existing guidance, largely due to the consideration to be given to unrecognized differences between the fair value and carrying values of the other assets and liabilities in the reporting unit under the new guidance. The amendments should be applied on a prospective basis. The update is effective for fiscal and interim periods beginning after December 15, 2019. Early adoption has been permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. Management is evaluating the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures. In August 2018, the FASB issued ASU 2018-15 “Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract.” The update generally aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement (that is a service contract) with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. Once capitalized, the update requires the entity to expense the amount capitalized over the term of the hosting arrangement, including reasonably certain renewal periods. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption of the amendments in this update is permitted for interim and related annual fiscal periods after December 15, 2018. Management is evaluating the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures. In August 2018, the FASB issued ASU 2018-14 “Compensation—Retirement Benefits—Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans.” This update removes disclosures that are no longer considered cost-beneficial, clarifies the specific requirements of disclosures, and adds disclosure requirements identified as relevant. The update applies to all employers that sponsor defined benefit pension or other postretirement plans. The update is effective for fiscal years ending after December 15, 2020. Upon adoption, the Company and Southwest will modify their disclosures to conform to the requirements of the update. In August 2018, the FASB issued ASU 2018-13 “Fair Value Measurement: Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement.” The update modifies the disclosure requirements on fair value measurements in Topic 820. The update is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32847-109319

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
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-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6491622&loc=d3e9504-115650

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-Paragraph 17
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32809-109319

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116657188&loc=SL116659661-227067

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32840-109319

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-URI http://asc.fasb.org/extlink&oid=116821951&loc=d3e32247-109318

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 05
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-URI http://asc.fasb.org/extlink&oid=65884525&loc=d3e40913-109327

+ Details

Background, Organization, and Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Other Property and Investments

Other Property and Investments. Other property and investments on the Condensed Consolidated Balance Sheets includes (thousands of dollars):



	September 30, 2019			December 31, 2018
Southwest Gas Corporation:
Net cash surrender value of COLI policies	$	126,142		$	114,405
Other property	1,632			1,741
Total Southwest Gas Corporation	127,774			116,146
Centuri property, equipment, and intangibles	968,013			792,191
Centuri accumulated depreciation/amortization	(345,113		)	(298,939		)
Other property	18,011			14,153
Total Southwest Gas Holdings, Inc.	$	768,685		$	623,551

Accounts Receivable for Services

Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars):



	September 30, 2019		December 31, 2018
Centuri accounts receivable for services provided to Southwest	$	16,757	$	18,830

Schedule of Goodwill



(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services			Total Company
December 31, 2018	$	10,095	$	348,950		$	359,045
Measurement-period adjustments - Linetec acquisition (a)	—		(22,179		)	(22,179		)
Foreign currency translation adjustment	—		3,082			3,082
September 30, 2019	$	10,095	$	329,853		$	339,948

(a) See Note 12 – Business Acquisitions for details regarding Linetec measurement-period adjustments.

Other Income (Deductions)



	Three Months Ended						Nine Months Ended						Twelve Months Ended
	September 30,						September 30,						September 30,
	2019			2018			2019			2018			2019			2018
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	200		$	4,700		$	11,200		$	6,000		$	2,000		$	9,500
Interest income	1,521			1,506			4,940			4,301			6,659			5,237
Equity AFUDC	1,212			448			3,179			1,034			5,772			1,253
Other components of net periodic benefit cost	(3,765		)	(5,265		)	(11,295		)	(15,794		)	(16,560		)	(20,650		)
Miscellaneous income and (expense)	(521		)	(553		)	(1,839		)	(1,402		)	(3,065		)	(1,765		)
Southwest Gas Corporation - total other income (deductions)	(1,353		)	836			6,185			(5,861		)	(5,194		)	(6,425		)
Utility infrastructure services segment:
Interest income	—			4			—			6			82			7
Foreign transaction gain (loss)	(6		)	(91		)	546			258			66			144
Miscellaneous income and (expense)	177			125			23			(595		)	514			(175		)
Centuri - total other income (deductions)	171			38			569			(331		)	662			(24		)
Corporate and administrative	24			15			73			41			84			48
Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	(1,158	)	$	889		$	6,827		$	(6,151	)	$	(4,448	)	$	(6,401	)

Components of Net Periodic Benefit Cost (Tables)

9 Months Ended

Sep. 30, 2019

Retirement Benefits [Abstract]

Schedule of Net Periodic Benefit Costs



	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	6,466		$	7,139		$	19,398		$	21,417		$	26,536		$	27,265
Interest cost	12,252			11,043			36,755			33,130			47,799			44,652
Expected return on plan assets	(15,061		)	(14,689		)	(45,183		)	(44,066		)	(59,872		)	(57,865		)
Amortization of net actuarial loss	5,589			8,029			16,767			24,086			24,796			30,087
Net periodic benefit cost	$	9,246		$	11,522		$	27,737		$	34,567		$	39,259		$	44,139

	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	66		$	61		$	199		$	183		$	261		$	260
Interest cost	440			415			1,320			1,244			1,734			1,714
Amortization of net actuarial loss	255			375			765			1,126			1,141			1,486
Net periodic benefit cost	$	761		$	851		$	2,284		$	2,553		$	3,136		$	3,460

	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2019			2018			2019			2018			2019			2018
(Thousands of dollars)
Service cost	$	319		$	368		$	957		$	1,105		$	1,325		$	1,472
Interest cost	761			687			2,285			2,061			2,972			2,869
Expected return on plan assets	(789		)	(929		)	(2,367		)	(2,789		)	(3,296		)	(3,629		)
Amortization of prior service costs	318			334			953			1,002			1,286			1,336
Net periodic benefit cost	$	609		$	460		$	1,828		$	1,379		$	2,287		$	2,048

Revenue (Tables)

9 Months Ended

Sep. 30, 2019

Revenue from Contract with Customer [Abstract]

Summary of Revenue Disaggregated by Service Type and Contract Type



	Three Months Ended				Nine Months Ended					Twelve Months Ended
	September 30,				September 30,					September 30,
(Thousands of dollars)	2019		2018		2019			2018		2019			2018
Residential	$	124,169	$	120,249	$	706,270		$	631,562	$	961,928		$	864,128
Small commercial	39,725		40,020		179,519			183,616		250,986			253,330
Large commercial	10,945		11,360		36,030			39,934		49,288			54,462
Industrial/other	3,837		5,390		15,728			17,391		21,826			23,899
Transportation	21,580		19,818		68,297			64,591		90,696			88,115
Revenue from contracts with customers	200,256		196,837		1,005,844			937,094		1,374,724			1,283,934
Alternative revenue program revenues (deferrals)	7,957		9,094		(23,196		)	46,696		(23,913		)	67,017
Other revenues (a)	1,767		11,592		6,720			3,725		8,770			3,049
Total Gas operating revenues	$	209,980	$	217,523	$	989,368		$	987,515	$	1,359,581		$	1,354,000



(Thousands of dollars)	Three Months Ended				Nine Months Ended				Twelve Months Ended
	September 30,				September 30,				September 30,
	2019		2018		2019		2018		2019		2018
Service Types:
Gas infrastructure services	$	364,241	$	355,721	$	885,950	$	849,615	$	1,160,017	$	1,145,629
Electric power infrastructure services	70,610		4,666		184,277		14,062		202,844		19,304
Other	80,399		90,236		212,185		242,167		335,992		314,859
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792



(Thousands of dollars)	Three Months Ended				Nine Months Ended				Twelve Months Ended
	September 30,				September 30,				September 30,
	2019		2018		2019		2018		2019		2018
Contract Types:
Master services agreement	$	410,283	$	348,274	$	1,021,798	$	832,813	$	1,291,397	$	1,101,216
Bid contract	104,967		102,349		260,614		273,031		407,456		378,576
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792

Unit price contracts	$	415,404	$	368,918	$	1,006,577	$	948,593	$	1,316,404	$	1,286,059
Fixed price contracts	37,539		45,461		80,503		44,911		152,890		31,487
Time and materials contracts	62,307		36,244		195,332		112,340		229,559		162,246
Total Utility infrastructure services revenues	$	515,250	$	450,623	$	1,282,412	$	1,105,844	$	1,698,853	$	1,479,792

Summary of Information about Receivables, Revenue Earned on Contracts in Progress in Excess of Billings, Which are Included Within Accounts Receivable, Net of Allowances, and Amounts Billed in Excess of Revenue Earned on Contracts



(Thousands of dollars)	September 30, 2019		December 31, 2018
Contracts receivable, net	$	238,678	$	186,249
Revenue earned on contracts in progress in excess of billings	121,854		87,520
Amounts billed in excess of revenue earned on contracts	6,136		4,211

Schedule of Construction Services Contracts Receivable

Utility infrastructure services contracts receivable consists of the following:



(Thousands of dollars)	September 30, 2019			December 31, 2018
Billed on completed contracts and contracts in progress	$	238,117		$	184,100
Other receivables	1,156			2,588
Contracts receivable, gross	239,273			186,688
Allowance for doubtful accounts	(595		)	(439		)
Contracts receivable, net	$	238,678		$	186,249

Leases (Tables)

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Components of Lease Expense, and Supplemental Cash Flow Information Related to Leases

The components of lease expense were as follows:



(Thousands of dollars)	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019
Southwest:
Operating lease cost	$	350	$	1,165

Centuri:
Operating lease cost	$	3,026	$	9,069

Finance lease cost:
Amortization of ROU assets	$	34	$	103
Interest on lease liabilities	10		24
Total finance lease cost	44		127
Short-term lease cost	5,017		10,949
Total lease cost	$	8,437	$	21,310

Supplemental cash flow information related to leases for the nine months ended September 30, 2019 is as follows:



(Thousands of dollars)	Southwest		Centuri		Consolidated Total
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$	976	$	8,104	$	9,080
Operating cash flows from finance leases	—		24		24
Financing cash flows from finance leases	—		161		161

ROU assets obtained in exchange for lease obligations:
Operating leases	$	1,143	$	21,653	$	22,796
Finance leases	—		386		386

Supplemental Information Related to Leases Included in Balance Sheet

Supplemental information related to leases, including location in the Condensed Consolidated Balance Sheets, is as follows:



(Thousands of dollars)	September 30, 2019
Southwest:
Operating leases:
Net Utility Plant	$	2,008

Other current liabilities	$	826
Other deferred credits and other long-term liabilities	1,209
Total operating lease liabilities	$	2,035

Weighted average remaining lease term (in years)	3.77
Weighted average discount rate	3.35		%

Centuri:
Operating leases:
Other property and investments	$	71,377

Other current liabilities	8,183
Other deferred credits and other long-term liabilities	65,791
Total operating lease liabilities	$	73,974

Finance leases:
Other property and investments	$	788

Other current liabilities	256
Other deferred credits and other long-term liabilities	400
Total finance lease liabilities	$	656

Weighted average remaining lease term (in years)
Operating leases	9.43
Finance leases	1.79

Weighted average discount rate
Operating leases	4.08		%
Finance leases	5.95		%

Schedule of Maturities of Operating Lease Liabilities

The following are schedules of maturities of lease liabilities as of September 30, 2019:



(Thousands of dollars)	Operating leases
Southwest:
2020	$	946
2021	548
2022	244
2023	79
2024	79
Thereafter	267
Total lease payments	2,163
Less imputed interest	128
Total	$	2,035



(Thousands of dollars)	Operating leases		Finance leases
Centuri:
2020	$	11,336	$	289
2021	10,416		174
2022	9,675		165
2023	8,192		95
2024	6,973		3
Thereafter	45,564		—
Total lease payments	92,156		726
Less imputed interest	18,182		70
Total	$	73,974	$	656

Schedule of Maturities of Finance Lease Liabilities

The following are schedules of maturities of lease liabilities as of September 30, 2019:



(Thousands of dollars)	Operating leases
Southwest:
2020	$	946
2021	548
2022	244
2023	79
2024	79
Thereafter	267
Total lease payments	2,163
Less imputed interest	128
Total	$	2,035



(Thousands of dollars)	Operating leases		Finance leases
Centuri:
2020	$	11,336	$	289
2021	10,416		174
2022	9,675		165
2023	8,192		95
2024	6,973		3
Thereafter	45,564		—
Total lease payments	92,156		726
Less imputed interest	18,182		70
Total	$	73,974	$	656

Schedule of Rental and Lease Payments



	2018		2017
Southwest Gas Corporation	$	4,556	$	4,926
Centuri	59,491		62,310
Consolidated rental payments/lease expense	$	64,047	$	67,236

Schedule of Future Minimum Rental Payments for Operating Leases

The following is a schedule of future minimum lease payments for operating leases (with initial or remaining terms in excess of one year) as of December 31, 2018 (thousands of dollars):



	Southwest		Centuri		Consolidated Total
2019	$	898	$	10,053	$	10,951
2020	363		7,656		8,019
2021	299		5,760		6,059
2022	163		5,163		5,326
2023	79		3,681		3,760
Thereafter	177		10,511		10,688
Total minimum lease payments	$	1,979	$	42,824	$	44,803

Derivatives (Tables)

9 Months Ended

Sep. 30, 2019

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Notional Amounts under Swaps Contracts

The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms):



	September 30, 2019	December 31, 2018
Contract notional amounts	16,071	13,387

Paid to and Received from Counterparties for Settlements of Matured Swaps

The following table shows the amounts Southwest paid to and received from counterparties for settlements of matured Swaps:



(Thousands of dollars)	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019		Twelve Months Ended September 30, 2019
Paid to counterparties	$	2,191	$	8,338	$	10,322
Received from counterparties	$	10	$	1,057	$	1,657

Fair Values of Swaps in Consolidated Balance Sheets

Fair values of derivatives not designated as hedging instruments:



September 30, 2019
Swap Position
Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total			Offsetting Balance Sheet Location (Regulatory Asset/(Liability))
Swaps	Deferred charges and other assets	$	48	$	(27	)	$	21		Other deferred credits
Swaps	Other current liabilities	103		(9,837		)	(9,734		)	Prepaid and other current assets
Swaps	Other deferred credits	—		(335		)	(335		)	Deferred charges and other assets
Total		$	151	$	(10,199	)	$	(10,048	)

December 31, 2018
Swap Position
Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total			Offsetting Balance Sheet Location (Regulatory Asset/(Liability))
Swaps	Prepaid and other current assets	$	243	$	(99	)	$	144		Other current liabilities
Swaps	Other current liabilities	1,595		(3,347		)	(1,752		)	Prepaid and other current assets
Swaps	Other deferred credits	141		(251		)	(110		)	Deferred charges and other assets
Total		$	1,979	$	(3,697	)	$	(1,718	)

Common Stock (Tables)

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

Schedule of Common Stock Activity

The following table provides the activity under the Equity Shelf Program for the quarter and life-to-date ended September 30, 2019:



	Three Months Ended			Life-To-Date Ended
	September 30,
	2019			2019
Gross proceeds	$	24,337,600		$	99,337,371
Less: agent commissions	(243,375		)	(993,373		)
Net proceeds	$	24,094,225		$	98,343,998

Number of shares sold	273,594			1,146,955
Weighted average price per share	$	88.96		$	86.61

Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt



	September 30, 2019					December 31, 2018
	Carrying Amount			Market Value		Carrying Amount			Market Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 4.45%, due 2020	$	125,000		$	126,763	$	125,000		$	126,213
Notes, 6.1%, due 2041	125,000			167,619		125,000			150,728
Notes, 3.875%, due 2022	250,000			257,930		250,000			254,195
Notes, 4.875%, due 2043	250,000			303,955		250,000			268,985
Notes, 3.8%, due 2046	300,000			316,383		300,000			267,030
Notes, 3.7%, due 2028	300,000			323,034		300,000			298,926
Notes, 4.15%, due 2049	300,000			334,680		—			—
8% Series, due 2026	75,000			97,769		75,000			93,827
Medium-term notes, 7.78% series, due 2022	25,000			27,655		25,000			27,497
Medium-term notes, 7.92% series, due 2027	25,000			32,250		25,000			30,016
Medium-term notes, 6.76% series, due 2027	7,500			9,218		7,500			8,651
Unamortized discount and debt issuance costs	(14,852		)			(11,807		)
	1,767,648					1,470,693
Revolving credit facility and commercial paper	150,000			150,000		150,000			150,000
Industrial development revenue bonds:
Variable-rate bonds:
Tax-exempt Series A, due 2028	50,000			50,000		50,000			50,000
2003 Series A, due 2038	50,000			50,000		50,000			50,000
2008 Series A, due 2038	50,000			50,000		50,000			50,000
2009 Series A, due 2039	50,000			50,000		50,000			50,000
Unamortized discount and debt issuance costs	(1,778		)			(2,024		)
	198,222					197,976
Less: current maturities	—					—
Long-term debt, less current maturities - Southwest Gas Corporation	$	2,115,870				$	1,818,669
Centuri:
Centuri term loan facility	$	248,043		$	257,475	$	255,959		$	260,135
Unamortized debt issuance costs	(1,171		)			(1,414		)
	246,872					254,545
Centuri secured revolving credit facility	89,140			89,175		—			—
Centuri other debt obligations	48,399			49,393		67,104			67,053
Less: current maturities	(38,165		)			(33,060		)
Long-term debt, less current maturities - Centuri	$	346,246				$	288,589
Consolidated Southwest Gas Holdings, Inc.:
Southwest Gas Corporation long-term debt	$	2,115,870				$	1,818,669
Centuri long-term debt	384,411					321,649
Less: current maturities	(38,165		)			(33,060		)
Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	2,462,116				$	2,107,258

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2019

Equity [Abstract]

(Thousands of dollars)



	Three Months Ended September 30, 2019									Three Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Amortization of prior service cost	$	318		$	(77	)	$	241		$	334		$	(80	)	$	254
Amortization of net actuarial (gain)/loss	5,844			(1,402		)	4,442			8,404			(2,017		)	6,387
Regulatory adjustment	(5,348		)	1,283			(4,065		)	(7,560		)	1,814			(5,746		)
Pension plans other comprehensive income	814			(196		)	618			1,178			(283		)	895
FSIRS (designated hedging activities):
Amounts reclassified into net income	836			(201		)	635			836			(200		)	636
FSIRS other comprehensive income	836			(201		)	635			836			(200		)	636
Total other comprehensive income - Southwest Gas Corporation	1,650			(397		)	1,253			2,014			(483		)	1,531
Foreign currency translation adjustments:
Translation adjustments	(447		)	—			(447		)	599			—			599
Foreign currency other comprehensive income (loss)	(447		)	—			(447		)	599			—			599
Total other comprehensive income - Southwest Gas Holdings, Inc.	$	1,203		$	(397	)	$	806		$	2,613		$	(483	)	$	2,130

	Nine Months Ended September 30, 2019									Nine Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Amortization of prior service cost	$	953		$	(229	)	$	724		$	1,002		$	(240	)	$	762
Amortization of net actuarial (gain)/loss	17,532			(4,207		)	13,325			25,212			(6,051		)	19,161
Regulatory adjustment	(16,043		)	3,850			(12,193		)	(22,679		)	5,443			(17,236		)
Pension plans other comprehensive income	2,442			(586		)	1,856			3,535			(848		)	2,687
FSIRS (designated hedging activities):
Amounts reclassified into net income	2,508			(602		)	1,906			2,509			(602		)	1,907
FSIRS other comprehensive income	2,508			(602		)	1,906			2,509			(602		)	1,907
Total other comprehensive income - Southwest Gas Corporation	4,950			(1,188		)	3,762			6,044			(1,450		)	4,594
Foreign currency translation adjustments:
Translation adjustments	1,131			—			1,131			(1,002		)	—			(1,002		)
Foreign currency other comprehensive income (loss)	1,131			—			1,131			(1,002		)	—			(1,002		)
Total other comprehensive income - Southwest Gas Holdings, Inc.	$	6,081		$	(1,188	)	$	4,893		$	5,042		$	(1,450	)	$	3,592



	Twelve Months Ended September 30, 2019									Twelve Months Ended September 30, 2018
	Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount			Before- Tax Amount			Tax (Expense) or Benefit (1)			Net-of- Tax Amount
Defined benefit pension plans:
Net actuarial gain/(loss)	$	(20,426	)	$	4,902		$	(15,524	)	$	(43,027	)	$	10,326		$	(32,701	)
Amortization of prior service cost	1,286			(309		)	977			1,336			(367		)	969
Amortization of net actuarial (gain)/loss	25,937			(6,224		)	19,713			31,573			(8,468		)	23,105
Regulatory adjustment	(1,597		)	383			(1,214		)	6,865			(844		)	6,021
Pension plans other comprehensive income (loss)	5,200			(1,248		)	3,952			(3,253		)	647			(2,606		)
FSIRS (designated hedging activities):
Amounts reclassified into net income	3,344			(804		)	2,540			3,346			(920		)	2,426
FSIRS other comprehensive income	3,344			(804		)	2,540			3,346			(920		)	2,426
Total other comprehensive income (loss) - Southwest Gas Corporation	8,544			(2,052		)	6,492			93			(273		)	(180		)
Foreign currency translation adjustments:
Translation adjustments	(877		)	—			(877		)	(1,092		)	—			(1,092		)
Foreign currency other comprehensive income (loss)	(877		)	—			(877		)	(1,092		)	—			(1,092		)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	7,667		$	(2,052	)	$	5,615		$	(999	)	$	(273	)	$	(1,272	)

(1)

Rollforward of Accumulated Other Comprehensive Income

The following table represents a rollforward of AOCI, presented on the Company’s Condensed Consolidated Balance Sheets (thousands of dollars):



	Defined Benefit Plans									FSIRS									Foreign Currency Items
	Before-Tax			Tax (Expense) Benefit (4,5)			After-Tax (5)			Before-Tax			Tax (Expense) Benefit (4,5)			After-Tax (5)			Before-Tax			Tax (Expense) Benefit		After-Tax			AOCI
Beginning Balance AOCI December 31, 2018	$	(55,227	)	$	13,254		$	(41,973	)	$	(9,310	)	$	2,234		$	(7,076	)	$	(3,619	)	$	—	$	(3,619	)	$	(52,668	)
Translation adjustments	—			—			—			—			—			—			1,131			—		1,131			1,131
Other comprehensive income (loss) before reclassifications	—			—			—			—			—			—			1,131			—		1,131			1,131
FSIRS amounts reclassified from AOCI (1)	—			—			—			2,508			(602		)	1,906						—		—			1,906
Amortization of prior service cost (2)	953			(229		)	724			—			—			—			—			—		—			724
Amortization of net actuarial loss (2)	17,532			(4,207		)	13,325			—			—			—			—			—		—			13,325
Regulatory adjustment (3)	(16,043		)	3,850			(12,193		)	—			—			—			—			—		—			(12,193		)
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	2,442			(586		)	1,856			2,508			(602		)	1,906			1,131			—		1,131			4,893
Ending Balance AOCI September 30, 2019	$	(52,785	)	$	12,668		$	(40,117	)	$	(6,802	)	$	1,632		$	(5,170	)	$	(2,488	)	$	—	$	(2,488	)	$	(47,775	)


(1)	The FSIRS reclassification amounts are included in Net interest deductions on the Company’s Condensed Consolidated Statements of Income.


(2)	These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost for additional details).


(3)	The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in Deferred charges and other assets on the Company’s Condensed Consolidated Balance Sheets).


(4)	Tax amounts are calculated using a 24% rate.


(5)	The beginning balances depict amounts attributable to the individual components of AOCI (Defined Benefit Plans and FSIRS) following the adoption of ASU No. 2018-02, with no impact to the total balance of AOCI resulting from the depiction.

The following table represents a rollforward of AOCI, presented on Southwest’s Condensed Consolidated Balance Sheets (thousands of dollars):



	Defined Benefit Plans									FSIRS
	Before-Tax			Tax (Expense) Benefit (9,10)			After-Tax (10)			Before-Tax			Tax (Expense) Benefit (9,10)			After-Tax (10)			AOCI
Beginning Balance AOCI December 31, 2018	$	(55,227	)	$	13,254		$	(41,973	)	$	(9,310	)	$	2,234		$	(7,076	)	$	(49,049	)
FSIRS amounts reclassified from AOCI (6)	—			—			—			2,508			(602		)	1,906			1,906
Amortization of prior service cost (7)	953			(229		)	724			—			—			—			724
Amortization of net actuarial loss (7)	17,532			(4,207		)	13,325			—			—			—			13,325
Regulatory adjustment (8)	(16,043		)	3,850			(12,193		)	—			—			—			(12,193		)
Net current period other comprehensive income attributable to Southwest Gas Corporation	2,442			(586		)	1,856			2,508			(602		)	1,906			3,762
Ending Balance AOCI September 30, 2019	$	(52,785	)	$	12,668		$	(40,117	)	$	(6,802	)	$	1,632		$	(5,170	)	$	(45,287	)


(6)	The FSIRS reclassification amounts are included in Net interest deductions on Southwest’s Condensed Consolidated Statements of Income.


(7)	These AOCI components are included in the computation of net periodic benefit cost (see Note 2 – Components of Net Periodic Benefit Cost for additional details).


(8)	The regulatory adjustment represents the portion of the activity above that is expected to be recovered through rates in the future (the related regulatory asset is included in Deferred charges and other assets on Southwest’s Condensed Consolidated Balance Sheets).


(9)	Tax amounts are calculated using a 24% rate.

(10)

The beginning balances depict amounts attributable to the individual components of AOCI (Defined Benefit Plans and FSIRS) following the adoption of ASU No. 2018-02, with no impact to the total balance of AOCI resulting from the depiction.

Amount Recognized Before Income Tax in Accumulated Other Comprehensive Income

The following table represents amounts (before income tax impacts) included in AOCI (in the tables above), that have not yet been recognized in net periodic benefit cost (thousands of dollars):



	September 30, 2019			December 31, 2018
Net actuarial (loss) gain	$	(417,832	)	$	(435,364	)
Prior service cost	(2,080		)	(3,033		)
Less: amount recognized in regulatory assets	367,127			383,170
Recognized in AOCI	$	(52,785	)	$	(55,227	)

Segment Information (Tables)

9 Months Ended

Sep. 30, 2019

Segment Reporting [Abstract]

Schedule of Segment Reporting Information

The following tables present revenues from external customers, intersegment revenues, and segment net income for the two reportable segments (thousands of dollars):



	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Three Months Ended September 30, 2019
Revenues from external customers	$	209,980		$	480,896	$	—		$	690,876
Intersegment revenues	—			34,354		—			34,354
Total	$	209,980		$	515,250	$	—		$	725,230
Segment net income (loss)	$	(20,012	)	$	25,838	$	(473	)	$	5,353

Three Months Ended September 30, 2018
Revenues from external customers	$	217,523		$	414,175	$	—		$	631,698
Intersegment revenues	—			36,448		—			36,448
Total	$	217,523		$	450,623	$	—		$	668,146
Segment net income (loss)	$	(13,670	)	$	26,798	$	(797	)	$	12,331

	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Nine Months Ended September 30, 2019
Revenues from external customers	$	989,368		$	1,160,303	$	—		$	2,149,671
Intersegment revenues	—			122,109		—			122,109
Total	$	989,368		$	1,282,412	$	—		$	2,271,780
Segment net income (loss)	$	86,746		$	36,725	$	(1,253	)	$	122,218

Nine Months Ended September 30, 2018
Revenues from external customers	$	987,515		$	1,009,166	$	—		$	1,996,681
Intersegment revenues	—			96,678		—			96,678
Total	$	987,515		$	1,105,844	$	—		$	2,093,359
Segment net income (loss)	$	79,301		$	35,034	$	(1,362	)	$	112,973

	Natural Gas Operations			Utility Infrastructure Services		Other			Total
Twelve Months Ended September 30, 2019
Revenues from external customers	$	1,359,581		$	1,537,508	$	—		$	2,897,089
Intersegment revenues	—			161,345		—			161,345
Total	$	1,359,581		$	1,698,853	$	—		$	3,058,434
Segment net income (loss)	$	146,287		$	46,668	$	(1,433	)	$	191,522

Twelve Months Ended September 30, 2018
Revenues from external customers	$	1,354,000		$	1,358,418	$	—		$	2,712,418
Intersegment revenues	—			121,374		—			121,374
Total	$	1,354,000		$	1,479,792	$	—		$	2,833,792
Segment net income (loss)	$	153,683		$	57,677	$	(1,922	)	$	209,438

Redeemable Noncontrolling Interests (Tables)

9 Months Ended

Sep. 30, 2019

Noncontrolling Interest [Abstract]

Summary of Redeemable Noncontrolling Interest

The following depicts the change to the balance of the redeemable noncontrolling interest:



(Thousands of dollars):	Redeemable Noncontrolling Interest
Balance, December 31, 2018	$	81,831
Net income attributable to redeemable noncontrolling interest	2,523
Balance, September 30, 2019	$	84,354

Business Acquisitions (Tables)

9 Months Ended

Sep. 30, 2019

Business Combinations [Abstract]

Summary of Fair Values of Assets Acquired and Liabilities Assumed

The preliminary estimated fair values of assets acquired and liabilities assumed as of November 30, 2018, are as follows (millions of dollars):



	Acquisition Date		Measurement Period Adjustments			Revised Acquisition Date
Cash and cash equivalents	$	3.9	$	—		$	3.9
Accounts receivable	32.8		(0.5		)	32.3
Revenue earned on contracts in progress in excess of billings	21.6		(0.2		)	21.4
Prepaid expenses and other current assets	1.1		0.1			1.2
Property and equipment	89.4		(0.8		)	88.6
Intangible assets	89.3		—			89.3
Goodwill	188.5		(22.2		)	166.3
Total assets acquired	426.6		(23.6		)	403.0

Accounts payable	8.0		—			8.0
Accrued liabilities	6.9		1.6			8.5
Deferred compensation and related accrued taxes	3.4		—			3.4
Redeemable noncontrolling interest	81.7		—			81.7
Total liabilities assumed and noncontrolling interest	100.0		1.6			101.6
Net assets acquired	$	326.6	$	(25.2	)	$	301.4

Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Other property	$ 18,011	$ 14,153
Total	768,685	623,551
Southwest Gas Corporation
Investment [Line Items]
Net cash surrender value of COLI policies	126,142	114,405
Other property	1,632	1,741
Total	127,774	116,146
Centuri
Investment [Line Items]
Centuri property, equipment, and intangibles	968,013	792,191
Centuri accumulated depreciation/amortization	$ (345,113)	$ (298,939)

Background, Organization, and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		9 Months Ended
	Nov. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Goodwill impairment		$ 0
Gas Pipe Materials and Supplies \| Prepaid and other current assets
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies		59,000,000	$ 56,000,000
Prepaid and other current assets		47,000,000	74,000,000
Pooled Funds and Mutual Funds \| Level 2 - Significant Other Observable Inputs
Significant Accounting Policies [Line Items]
Money market fund investments		10,200,000	59,900,000
Centuri \| Linetec
Significant Accounting Policies [Line Items]
Percentage of voting interests acquired	80.00%
Purchase consideration	$ 26,200,000
Southwest Gas Corporation
Significant Accounting Policies [Line Items]
Dividends declared but not yet paid		24,900,000	23,500,000
Southwest Gas Corporation \| Pooled Funds and Mutual Funds \| Level 2 - Significant Other Observable Inputs
Significant Accounting Policies [Line Items]
Money market fund investments		$ 1,500,000	$ 18,000,000

Background, Organization, and Summary of Significant Accounting Policies - Accounts Receivable for Services (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Centuri
Segment Reporting Information [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 16,757	$ 18,830

Background, Organization, and Summary of Significant Accounting Policies - Schedule of Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 359,045
Foreign currency translation adjustment	3,082
Goodwill, ending balance	339,948
Natural Gas Operations
Goodwill [Roll Forward]
Goodwill, beginning balance	10,095
Foreign currency translation adjustment	0
Goodwill, ending balance	10,095
Utility Infrastructure Services
Goodwill [Roll Forward]
Goodwill, beginning balance	348,950
Foreign currency translation adjustment	3,082
Goodwill, ending balance	329,853
Linetec
Goodwill [Roll Forward]
Measurement-period adjustments - Linetec acquisition (a)	(22,179)
Goodwill, ending balance	166,300
Linetec \| Natural Gas Operations
Goodwill [Roll Forward]
Measurement-period adjustments - Linetec acquisition (a)	0
Linetec \| Utility Infrastructure Services
Goodwill [Roll Forward]
Measurement-period adjustments - Linetec acquisition (a)	$ (22,179)

Background, Organization, and Summary of Significant Accounting Policies- Other Income (Deductions) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other income (deductions)
Total other income (deductions)	$ (1,158)	$ 889	$ 6,827	$ (6,151)	$ (4,448)	$ (6,401)
Southwest Gas Corporation
Other income (deductions)
Total other income (deductions)	(1,353)	836	6,185	(5,861)	(5,194)	(6,425)
Operating Segments \| Natural Gas Operations \| Southwest Gas Corporation
Other income (deductions)
Change in COLI policies	200	4,700	11,200	6,000	2,000	9,500
Interest income	1,521	1,506	4,940	4,301	6,659	5,237
Equity AFUDC	1,212	448	3,179	1,034	5,772	1,253
Other components of net periodic benefit cost	(3,765)	(5,265)	(11,295)	(15,794)	(16,560)	(20,650)
Miscellaneous income and (expense)	(521)	(553)	(1,839)	(1,402)	(3,065)	(1,765)
Total other income (deductions)	(1,353)	836	6,185	(5,861)	(5,194)	(6,425)
Operating Segments \| Utility Infrastructure Services \| Centuri
Other income (deductions)
Interest income	0	4	0	6	82	7
Foreign transaction gain (loss)	(6)	(91)	546	258	66	144
Miscellaneous income and (expense)	177	125	23	(595)	514	(175)
Total other income (deductions)	171	38	569	(331)	662	(24)
Corporate and administrative
Other income (deductions)
Total other income (deductions)	$ 24	$ 15	$ 73	$ 41	$ 84	$ 48

Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Qualified Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,466	$ 7,139	$ 19,398	$ 21,417	$ 26,536	$ 27,265
Interest cost	12,252	11,043	36,755	33,130	47,799	44,652
Expected return on plan assets	(15,061)	(14,689)	(45,183)	(44,066)	(59,872)	(57,865)
Amortization of net actuarial loss	5,589	8,029	16,767	24,086	24,796	30,087
Net periodic benefit cost	9,246	11,522	27,737	34,567	39,259	44,139
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost	66	61	199	183	261	260
Interest cost	440	415	1,320	1,244	1,734	1,714
Amortization of net actuarial loss	255	375	765	1,126	1,141	1,486
Net periodic benefit cost	761	851	2,284	2,553	3,136	3,460
PBOP
Defined Benefit Plan Disclosure [Line Items]
Service cost	319	368	957	1,105	1,325	1,472
Interest cost	761	687	2,285	2,061	2,972	2,869
Expected return on plan assets	(789)	(929)	(2,367)	(2,789)	(3,296)	(3,629)
Amortization of prior service costs	318	334	953	1,002	1,286	1,336
Net periodic benefit cost	$ 609	$ 460	$ 1,828	$ 1,379	$ 2,287	$ 2,048

Revenue - Additional Information (Detail) $ in Millions	9 Months Ended
Revenue - Additional Information (Detail) $ in Millions	Sep. 30, 2019 USD ($) Segment Contract
Southwest Gas Corporation
Segment Reporting Information [Line Items]
Number of operating segment \| Segment	1
Centuri
Segment Reporting Information [Line Items]
Change in contract liability, revenue recognized \| $	$ 4.2
Number of contracts with original duration more than one year \| Contract	53

Revenue - Revenue Performance Obligation (Details) - Centuri - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 $ in Millions	Sep. 30, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price allocated to unsatisfied performance obligations of contracts	$ 103.3
Revenue, remaining performance obligation, expected timing of satisfaction, period	2 years

Revenue - Schedule of Gas Operating Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 200,256	$ 196,837	$ 1,005,844	$ 937,094	$ 1,374,724	$ 1,283,934
Alternative revenue program revenues (deferrals)	7,957	9,094	(23,196)	46,696	(23,913)	67,017
Other revenues	1,767	11,592	6,720	3,725	8,770	3,049
Total Gas operating revenues	209,980	217,523	989,368	987,515	1,359,581	1,354,000
Tax Reform Savings Revenue Adjustments
Disaggregation of Revenue [Line Items]
Other revenues	(800)	(1,000)	(3,700)	(13,500)	(3,700)	(13,500)
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	124,169	120,249	706,270	631,562	961,928	864,128
Small commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39,725	40,020	179,519	183,616	250,986	253,330
Large commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10,945	11,360	36,030	39,934	49,288	54,462
Industrial/other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,837	5,390	15,728	17,391	21,826	23,899
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 21,580	$ 19,818	$ 68,297	$ 64,591	$ 90,696	$ 88,115

Revenue - Summary of Revenue Disaggregated by Service Type, and Contract Type (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 200,256	$ 196,837	$ 1,005,844	$ 937,094	$ 1,374,724	$ 1,283,934
Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	515,250	450,623	1,282,412	1,105,844	1,698,853	1,479,792
Master services agreement \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	410,283	348,274	1,021,798	832,813	1,291,397	1,101,216
Bid contract \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	104,967	102,349	260,614	273,031	407,456	378,576
Unit price contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	415,404	368,918	1,006,577	948,593	1,316,404	1,286,059
Fixed price contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37,539	45,461	80,503	44,911	152,890	31,487
Time and materials contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62,307	36,244	195,332	112,340	229,559	162,246
Gas infrastructure services \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	364,241	355,721	885,950	849,615	1,160,017	1,145,629
Electric power infrastructure services \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	70,610	4,666	184,277	14,062	202,844	19,304
Other \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 80,399	$ 90,236	$ 212,185	$ 242,167	$ 335,992	$ 314,859

Revenue - Summary of Information about Receivables (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contracts receivable, net	$ 238,678	$ 186,249
Revenue earned on contracts in progress in excess of billings	121,854	87,520
Amounts billed in excess of revenue earned on contracts	$ 6,136	$ 4,211

Revenue - Schedule of Construction Services Contracts Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Billed on completed contracts and contracts in progress	$ 238,117	$ 184,100
Other receivables	1,156	2,588
Contracts receivable, gross	239,273	186,688
Allowance for doubtful accounts	(595)	(439)
Contracts receivable, net	$ 238,678	$ 186,249

Leases - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 2,008
Lease liabilities	$ 2,035
Lease renewal term (up to)	3 years
Southwest Gas Corporation \| Minimum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	1 year
Southwest Gas Corporation \| Maximum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	10 years
Centuri
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 71,377
Lease liabilities	$ 73,974
Lease renewal term (up to)	5 years
Lease termination period	1 year
Short-term lease total future lease payments	$ 13,200
Centuri \| Maximum
Lessee, Lease, Description [Line Items]
Lease remaining lease term	19 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		$ 58,400
Lease liabilities		60,800
Accounting Standards Update 2016-02 \| Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets		1,900
Lease liabilities		$ 1,900

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Total lease cost	$ 8,437	$ 21,310
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease cost	350	1,165
Centuri
Lessee, Lease, Description [Line Items]
Operating lease cost	3,026	9,069
Amortization of ROU assets	34	103
Interest on lease liabilities	10	24
Total finance lease cost	44	127
Short-term lease cost	$ 5,017	$ 10,949

Leases - Supplemental Cash Flow Information Related to Leases (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating cash flows from operating leases	$ 9,080
Operating cash flows from finance leases	24
Financing cash flows from finance leases	161
ROU assets obtained in exchange for operating leases obligations	22,796
ROU assets obtained in exchange for finance leases obligations	386
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating cash flows from operating leases	976
Operating cash flows from finance leases	0
Financing cash flows from finance leases	0
ROU assets obtained in exchange for operating leases obligations	1,143
ROU assets obtained in exchange for finance leases obligations	0
Centuri
Lessee, Lease, Description [Line Items]
Operating cash flows from operating leases	8,104
Operating cash flows from finance leases	24
Financing cash flows from finance leases	161
ROU assets obtained in exchange for operating leases obligations	21,653
ROU assets obtained in exchange for finance leases obligations	$ 386

Leases - Supplemental Information Related to Leases Included in Balance Sheet (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, weighted average remaining lease term (in years)	9 years 5 months 4 days
Operating lease, weighted average discount rate	4.08%
Finance lease ROU assets	$ 788
Finance lease liabilities, current	256
Finance lease liabilities, noncurrent	400
Finance lease liabilities	$ 656
Finance lease, weighted average remaining lease term (in years)	1 year 9 months 14 days
Finance lease, weighted average discount rate	5.95%
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 2,008
Operating lease liabilities, current	826
Operating lease liabilities, noncurrent	1,209
Operating lease liabilities	$ 2,035
Operating lease, weighted average remaining lease term (in years)	3 years 9 months 7 days
Operating lease, weighted average discount rate	3.35%
Centuri
Lessee, Lease, Description [Line Items]
Operating lease ROU assets	$ 71,377
Operating lease liabilities, current	8,183
Operating lease liabilities, noncurrent	65,791
Operating lease liabilities	73,974
Finance lease liabilities	$ 656

Leases - Schedule of Maturities of Lease Liabilities (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Finance leases
Total	$ 656
Centuri
Operating leases
2020	11,336
2021	10,416
2022	9,675
2023	8,192
2024	6,973
Thereafter	45,564
Total lease payments	92,156
Less imputed interest	18,182
Total	73,974
Finance leases
2020	289
2021	174
2022	165
2023	95
2024	3
Thereafter	0
Total lease payments	726
Less imputed interest	70
Total	656
Southwest Gas Corporation
Operating leases
2020	946
2021	548
2022	244
2023	79
2024	79
Thereafter	267
Total lease payments	2,163
Less imputed interest	128
Total	$ 2,035

Leases - Schedule of Rental and Lease Payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	$ 64,047	$ 67,236
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	4,556	4,926
Centuri
Lessee, Lease, Description [Line Items]
Rental payments/lease expense	$ 59,491	$ 62,310

Leases - Schedule of Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items]
2019	$ 10,951
2020	8,019
2021	6,059
2022	5,326
2023	3,760
Thereafter	10,688
Total minimum lease payments	44,803
Southwest Gas Corporation
Lessee, Lease, Description [Line Items]
2019	898
2020	363
2021	299
2022	163
2023	79
Thereafter	177
Total minimum lease payments	1,979
Centuri
Lessee, Lease, Description [Line Items]
2019	10,053
2020	7,656
2021	5,760
2022	5,163
2023	3,681
Thereafter	10,511
Total minimum lease payments	$ 42,824

Derivatives - Notional Amounts under Swaps Contracts (Detail) - MMBTU MMBTU in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Contract notional amounts	16,071	13,387

Derivatives - Paid to and Received from Counterparties for Settlements of Matured Swaps (Detail) - Southwest Gas Corporation - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2019
Derivative [Line Items]
Paid to counterparties	$ 2,191	$ 8,338	$ 10,322
Received from counterparties	$ 10	$ 1,057	$ 1,657

Derivatives - Swaps in Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 151	$ 1,979
Liability derivatives not designated as hedging instruments	(10,199)	(3,697)
Net total not designated as hedging instruments	(10,048)	(1,718)
Swaps \| Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	48
Liability derivatives not designated as hedging instruments	(27)
Net total not designated as hedging instruments	21
Swaps \| Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments		243
Liability derivatives not designated as hedging instruments		(99)
Net total not designated as hedging instruments		144
Swaps \| Other current liabilities
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	103	1,595
Liability derivatives not designated as hedging instruments	(9,837)	(3,347)
Net total not designated as hedging instruments	(9,734)	(1,752)
Swaps \| Other deferred credits
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	0	141
Liability derivatives not designated as hedging instruments	(335)	(251)
Net total not designated as hedging instruments	$ (335)	$ (110)

Derivatives - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative collateral outstanding	$ 0	$ 0

Common Stock (Detail) - USD ($)	3 Months Ended		5 Months Ended	9 Months Ended		12 Months Ended
Common Stock (Detail) - USD ($)	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 20, 2019	Sep. 19, 2019	May 08, 2019
Class of Stock [Line Items]
Net proceeds to company				$ 129,341,000	$ 92,234,000	$ 391,509,000	$ 121,826,000
Common stock available for issuance (in shares)								120,000,000	60,000,000
Restricted Stock/Unit Plan, and Management Incentive Plan
Class of Stock [Line Items]
Common stock issued (in shares)				76,000
Dividend Reinvestment and Stock Purchase Plan
Class of Stock [Line Items]
Common stock issued (in shares)				96,000
Common stock issued, amount				$ 8,100,000
Equity Shelf Program
Class of Stock [Line Items]
Sale of stock, maximum amount of stock allowed to be offered										300,000,000
Gross proceeds	$ 24,337,600		$ 99,337,371
Agent commissions	(243,375)		(993,373)
Net proceeds to company	$ 24,094,225		$ 98,343,998
Number of shares sold (in shares)	273,594		1,146,955
Weighted average price per share	$ 88.96		$ 86.61
Sale of stock, common stock available for sale	$ 200,662,629		$ 200,662,629	$ 200,662,629		$ 200,662,629
Sale of stock, number of shares sold (in shares)		278,000

Long-Term Debt - Schedule of Long-Term Debt (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Line of credit facility	$ 0
Less: current maturities	(38,165,000)	$ (33,060,000)
Long-term debt, less current maturities	2,462,116,000	2,107,258,000
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(38,165,000)	(33,060,000)
Long-term debt, less current maturities	2,462,116,000	2,107,258,000
Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, less current maturities	2,115,870,000	1,818,669,000
Long-term Debt, Current and Noncurrent Abstract
Long-term debt, less current maturities	$ 2,115,870,000	$ 1,818,669,000
Debentures \| Notes, 4.45%, due 2020 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	4.45%	4.45%
Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	6.10%	6.10%
Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	3.875%	3.875%
Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	4.875%	4.875%
Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	3.80%	3.80%
Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	3.70%	3.70%
Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	4.15%
Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	8.00%	8.00%
Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	7.78%	7.78%
Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	7.92%	7.92%
Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Long-term Debt, Current and Noncurrent Abstract
Debt instrument interest rate	6.76%	6.76%
Carrying Amount
Debt Instrument [Line Items]
Long-term debt, less current maturities	$ 2,462,116,000	$ 2,107,258,000
Long-term Debt, Current and Noncurrent Abstract
Long-term debt, less current maturities	2,462,116,000	2,107,258,000
Carrying Amount \| Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	0	0
Long-term debt, less current maturities	2,115,870,000	1,818,669,000
Long-term Debt, Current and Noncurrent Abstract
Long-term debt	2,115,870,000	1,818,669,000
Less: current maturities	0	0
Long-term debt, less current maturities	2,115,870,000	1,818,669,000
Carrying Amount \| Centuri
Debt Instrument [Line Items]
Less: current maturities	(38,165,000)	(33,060,000)
Long-term debt, less current maturities	346,246,000	288,589,000
Unamortized debt issuance costs	(1,171,000)	(1,414,000)
Long-term Debt, Current and Noncurrent Abstract
Long-term debt	384,411,000	321,649,000
Less: current maturities	(38,165,000)	(33,060,000)
Long-term debt, less current maturities	346,246,000	288,589,000
Centuri secured revolving credit facility	246,872,000	254,545,000
Carrying Amount \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	89,140,000	0
Carrying Amount \| Centuri term loan facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	248,043,000	255,959,000
Carrying Amount \| Centuri other debt obligations \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	48,399,000	67,104,000
Carrying Amount \| Debentures \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	1,767,648,000	1,470,693,000
Unamortized discount and debt issuance costs	(14,852,000)	(11,807,000)
Carrying Amount \| Debentures \| Notes, 4.45%, due 2020 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	125,000,000	125,000,000
Carrying Amount \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	125,000,000	125,000,000
Carrying Amount \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000,000	250,000,000
Carrying Amount \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000,000	250,000,000
Carrying Amount \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000,000	300,000,000
Carrying Amount \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000,000	300,000,000
Carrying Amount \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000,000	0
Carrying Amount \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	75,000,000	75,000,000
Carrying Amount \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000,000	25,000,000
Carrying Amount \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000,000	25,000,000
Carrying Amount \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	7,500,000	7,500,000
Carrying Amount \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility	150,000,000	150,000,000
Carrying Amount \| Industrial development revenue bonds \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(1,778,000)	(2,024,000)
Unsecured debt	198,222,000	197,976,000
Carrying Amount \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Carrying Amount \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Carrying Amount \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Carrying Amount \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Market Value \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	257,475,000	260,135,000
Centuri other debt obligations	49,393,000	67,053,000
Market Value \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	89,175,000	0
Market Value \| Debentures \| Notes, 4.45%, due 2020 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	126,763,000	126,213,000
Market Value \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	167,619,000	150,728,000
Market Value \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	257,930,000	254,195,000
Market Value \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	303,955,000	268,985,000
Market Value \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	316,383,000	267,030,000
Market Value \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	323,034,000	298,926,000
Market Value \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	334,680,000	0
Market Value \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	97,769,000	93,827,000
Market Value \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	27,655,000	27,497,000
Market Value \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	32,250,000	30,016,000
Market Value \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	9,218,000	8,651,000
Market Value \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility, fair value	150,000,000	150,000,000
Market Value \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Market Value \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000,000	50,000,000
Market Value \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	50,000,000	50,000,000
Market Value \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	$ 50,000,000	$ 50,000,000

Long-Term Debt - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	May 31, 2019	Dec. 31, 2018	Nov. 30, 2018	Oct. 31, 2018
Debt Instrument [Line Items]
Short term borrowings outstanding	$ 30,000,000		$ 152,000,000
Borrowings outstanding under facility	$ 0
Percentage of total debt with interest rates reference to LIBOR and due after 2021	14.00%
Southwest Gas Corporation
Debt Instrument [Line Items]
Short term borrowings outstanding	$ 30,000,000		$ 152,000,000
Percentage of total debt with interest rates reference to LIBOR and due after 2021	6.00%
LIBOR
Debt Instrument [Line Items]
Borrowings outstanding under facility	$ 348,000,000
LIBOR \| Southwest Gas Corporation
Debt Instrument [Line Items]
Borrowings outstanding under facility	130,000,000
LIBOR \| Centuri
Debt Instrument [Line Items]
Borrowings outstanding under facility	218,000,000
Commercial Paper Program \| Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	50,000,000
Borrowings outstanding under facility	50,000,000
Secured Revolving Credit Facility and Term Loan \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				$ 590,000,000	$ 450,000,000
Borrowings outstanding under facility	337,000,000
Debt secured by assets	$ 1,300,000,000
Line of Credit \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				325,000,000
Centuri term loan facility \| Centuri
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				$ 265,000,000
Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt face amount		$ 300,000,000
Debt instrument interest rate	4.15%
Debt discount rate	0.051%
$400 Million Credit Facility \| Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 400,000,000
Line of credit designated as long term debt	150,000,000
Line of credit designated for working capital purposes	250,000,000
Long-term debt	150,000,000
Short term borrowings outstanding	$ 30,000,000
$400 Million Credit Facility \| LIBOR \| Southwest Gas Corporation
Debt Instrument [Line Items]
Applicable margin	1.00%
$400 Million Credit Facility \| Alternative Base Rate \| Southwest Gas Corporation
Debt Instrument [Line Items]
Applicable margin	0.00%

Short-Term Debt (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Short term borrowings outstanding	$ 30,000,000	$ 152,000,000
Southwest Gas Corporation
Short-term Debt [Line Items]
Short term borrowings outstanding	30,000,000	$ 152,000,000
Southwest Gas Corporation \| $100 Million Credit Facility
Short-term Debt [Line Items]
Credit facility maximum borrowing capacity	100,000,000
Short term borrowings outstanding	0
Southwest Gas Corporation \| $400 Million Credit Facility
Short-term Debt [Line Items]
Credit facility maximum borrowing capacity	400,000,000
Short term borrowings outstanding	30,000,000
Line of credit designated for working capital purposes	$ 250,000,000

Other Comprehensive Income and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to OCI (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, net of tax			$ 1,131
Other comprehensive income (loss), before tax	$ 1,203	$ 2,613	6,081	$ 5,042	$ 7,667	$ (999)
Other comprehensive income (loss), tax	(397)	(483)	(1,188)	(1,450)	(2,052)	(273)
Total other comprehensive income (loss), net of tax	806	2,130	$ 4,893	3,592	$ 5,615	$ (1,272)
Effective income tax rate			24.00%		24.00%	38.00%
Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	1,650	2,014	$ 4,950	6,044	$ 8,544	$ 93
Other comprehensive income (loss), tax	(397)	(483)	(1,188)	(1,450)	(2,052)	(273)
Total other comprehensive income (loss), net of tax	1,253	1,531	3,762	4,594	6,492	(180)
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	814	1,178	2,442	3,535	5,200	(3,253)
Other comprehensive income (loss), tax	(196)	(283)	(586)	(848)	(1,248)	647
Total other comprehensive income (loss), net of tax	618	895	1,856	2,687	3,952	(2,606)
Defined Benefit Plans \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			2,442
Other comprehensive income (loss), tax			(586)
Total other comprehensive income (loss), net of tax			1,856
Amortization of prior service cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	318	334	953	1,002	1,286	1,336
Reclassification from AOCI, tax	(77)	(80)	(229)	(240)	(309)	(367)
Reclassification from AOCI, net of tax	241	254	724	762	977	969
Other comprehensive income (loss), before tax			953
Other comprehensive income (loss), tax			(229)
Total other comprehensive income (loss), net of tax			724
Amortization of prior service cost \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			953
Other comprehensive income (loss), tax			(229)
Total other comprehensive income (loss), net of tax			724
Net actuarial gain/(loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, before tax					(20,426)	(43,027)
Other comprehensive income (loss) before reclassifications, tax					4,902	10,326
Other comprehensive income (loss) before reclassifications, net of tax					(15,524)	(32,701)
Reclassification from AOCI, before Tax	5,844	8,404	17,532	25,212	25,937	31,573
Reclassification from AOCI, tax	(1,402)	(2,017)	(4,207)	(6,051)	(6,224)	(8,468)
Reclassification from AOCI, net of tax	4,442	6,387	13,325	19,161	19,713	23,105
Other comprehensive income (loss), before tax			17,532
Other comprehensive income (loss), tax			(4,207)
Total other comprehensive income (loss), net of tax			13,325
Net actuarial gain/(loss) \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			17,532
Other comprehensive income (loss), tax			(4,207)
Total other comprehensive income (loss), net of tax			13,325
Regulatory adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	(5,348)	(7,560)	(16,043)	(22,679)	(1,597)	6,865
Reclassification from AOCI, tax	1,283	1,814	3,850	5,443	383	(844)
Reclassification from AOCI, net of tax	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Other comprehensive income (loss), before tax			(16,043)
Other comprehensive income (loss), tax			3,850
Total other comprehensive income (loss), net of tax			(12,193)
Regulatory adjustment \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			(16,043)
Other comprehensive income (loss), tax			3,850
Total other comprehensive income (loss), net of tax			(12,193)
FSIRS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	836	836	2,508	2,509	3,344	3,346
Reclassification from AOCI, tax	(201)	(200)	(602)	(602)	(804)	(920)
Reclassification from AOCI, net of tax	635	636	1,906	1,907	2,540	2,426
Other comprehensive income (loss), before tax	836	836	2,508	2,509	3,344	3,346
Other comprehensive income (loss), tax	(201)	(200)	(602)	(602)	(804)	(920)
Total other comprehensive income (loss), net of tax	635	636	1,906	1,907	2,540	2,426
FSIRS \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax			2,508
Reclassification from AOCI, tax			(602)
Reclassification from AOCI, net of tax			1,906
Other comprehensive income (loss), before tax			2,508
Other comprehensive income (loss), tax			(602)
Total other comprehensive income (loss), net of tax			1,906
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, before tax	(447)	599	1,131	(1,002)	(877)	(1,092)
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0	0	0
Other comprehensive income (loss) before reclassifications, net of tax	$ (447)	$ 599	1,131	$ (1,002)	$ (877)	$ (1,092)
Other comprehensive income (loss), before tax			1,131
Total other comprehensive income (loss), net of tax			$ 1,131

Other Comprehensive Income and Accumulated Other Comprehensive Income - Additional Information (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Equity [Abstract]
Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months	$ 2.5

Other Comprehensive Income and Accumulated Other Comprehensive Income - AOCI Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 2,251,590		$ 1,945,781
Beginning balance, attributable to parent			2,252,042
Other comprehensive income (loss) before reclassifications, net of tax			1,131
Other comprehensive income (loss), before tax	$ 1,203	$ 2,613	6,081	$ 5,042	7,667	$ (999)
Other comprehensive income (loss), tax	(397)	(483)	(1,188)	(1,450)	(2,052)	(273)
Total other comprehensive income (loss), net of tax	806	2,130	4,893	3,592	5,615	(1,272)
Ending balance, attributable to parent	2,423,710		2,423,710		2,423,710
Ending balance	2,423,710	1,945,781	$ 2,423,710	1,945,781	$ 2,423,710	$ 1,945,781
Effective income tax rate			24.00%		24.00%	38.00%
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			$ (55,227)
Beginning balance, tax			13,254
Beginning balance			(41,973)
Other comprehensive income (loss), before tax	814	1,178	2,442	3,535	$ 5,200	$ (3,253)
Other comprehensive income (loss), tax	(196)	(283)	(586)	(848)	(1,248)	647
Total other comprehensive income (loss), net of tax	618	895	1,856	2,687	3,952	(2,606)
Ending balance, before tax	(52,785)		(52,785)		(52,785)
Ending balance, tax	12,668		12,668		12,668
Ending balance	(40,117)		(40,117)		(40,117)
Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	318	334	953	1,002	1,286	1,336
Reclassification from AOCI, tax	(77)	(80)	(229)	(240)	(309)	(367)
Reclassification from AOCI, net of tax	241	254	724	762	977	969
Other comprehensive income (loss), before tax			953
Other comprehensive income (loss), tax			(229)
Total other comprehensive income (loss), net of tax			724
Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, before tax					(20,426)	(43,027)
Other comprehensive income (loss) before reclassifications, net of tax					(15,524)	(32,701)
Reclassification from AOCI, before Tax	5,844	8,404	17,532	25,212	25,937	31,573
Reclassification from AOCI, tax	(1,402)	(2,017)	(4,207)	(6,051)	(6,224)	(8,468)
Reclassification from AOCI, net of tax	4,442	6,387	13,325	19,161	19,713	23,105
Other comprehensive income (loss), before tax			17,532
Other comprehensive income (loss), tax			(4,207)
Total other comprehensive income (loss), net of tax			13,325
Regulatory adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	(5,348)	(7,560)	(16,043)	(22,679)	(1,597)	6,865
Reclassification from AOCI, tax	1,283	1,814	3,850	5,443	383	(844)
Reclassification from AOCI, net of tax	(4,065)	(5,746)	(12,193)	(17,236)	(1,214)	6,021
Other comprehensive income (loss), before tax			(16,043)
Other comprehensive income (loss), tax			3,850
Total other comprehensive income (loss), net of tax			(12,193)
FSIRS
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			(9,310)
Beginning balance, tax			2,234
Beginning balance			(7,076)
Reclassification from AOCI, before Tax	836	836	2,508	2,509	3,344	3,346
Reclassification from AOCI, tax	(201)	(200)	(602)	(602)	(804)	(920)
Reclassification from AOCI, net of tax	635	636	1,906	1,907	2,540	2,426
Other comprehensive income (loss), before tax	836	836	2,508	2,509	3,344	3,346
Other comprehensive income (loss), tax	(201)	(200)	(602)	(602)	(804)	(920)
Total other comprehensive income (loss), net of tax	635	636	1,906	1,907	2,540	2,426
Ending balance, before tax	(6,802)		(6,802)		(6,802)
Ending balance, tax	1,632		1,632		1,632
Ending balance	(5,170)		(5,170)		(5,170)
Foreign Currency Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			(3,619)
Beginning balance			(3,619)
Other comprehensive income (loss) before reclassifications, before tax	(447)	599	1,131	(1,002)	(877)	(1,092)
Other comprehensive income (loss) before reclassifications, net of tax	(447)	599	1,131	(1,002)	(877)	(1,092)
Other comprehensive income (loss), before tax			1,131
Total other comprehensive income (loss), net of tax			1,131
Ending balance, before tax	(2,488)		(2,488)		(2,488)
Ending balance	(2,488)		(2,488)		(2,488)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(48,581)	(55,520)	(52,668)	(47,682)	(53,390)
Ending balance	(47,775)	(53,390)	(47,775)	(53,390)	(47,775)	(53,390)
Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance					1,719,927
Beginning balance, attributable to parent			1,782,460
Other comprehensive income (loss), before tax	1,650	2,014	4,950	6,044	8,544	93
Other comprehensive income (loss), tax	(397)	(483)	(1,188)	(1,450)	(2,052)	(273)
Total other comprehensive income (loss), net of tax	1,253	1,531	3,762	4,594	6,492	(180)
Ending balance, attributable to parent	1,929,606		1,929,606		1,929,606
Ending balance	1,929,606	1,719,927	1,929,606	1,719,927	1,929,606	1,719,927
Southwest Gas Corporation \| Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent, before tax			(55,227)
Beginning balance, attributable to parent, tax			13,254
Beginning balance, attributable to parent			(41,973)
Other comprehensive income (loss), before tax			2,442
Other comprehensive income (loss), tax			(586)
Total other comprehensive income (loss), net of tax			1,856
Ending balance, attributable to parent, before tax	(52,785)		(52,785)		(52,785)
Ending balance, attributable to parent, tax	12,668		12,668		12,668
Ending balance, attributable to parent	(40,117)		(40,117)		(40,117)
Southwest Gas Corporation \| Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			953
Other comprehensive income (loss), tax			(229)
Total other comprehensive income (loss), net of tax			724
Southwest Gas Corporation \| Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			17,532
Other comprehensive income (loss), tax			(4,207)
Total other comprehensive income (loss), net of tax			13,325
Southwest Gas Corporation \| Regulatory adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			(16,043)
Other comprehensive income (loss), tax			3,850
Total other comprehensive income (loss), net of tax			(12,193)
Southwest Gas Corporation \| FSIRS
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent, before tax			(9,310)
Beginning balance, attributable to parent, tax			2,234
Beginning balance, attributable to parent			(7,076)
Reclassification from AOCI, before Tax			2,508
Reclassification from AOCI, tax			(602)
Reclassification from AOCI, net of tax			1,906
Other comprehensive income (loss), before tax			2,508
Other comprehensive income (loss), tax			(602)
Total other comprehensive income (loss), net of tax			1,906
Ending balance, attributable to parent, before tax	(6,802)		(6,802)		(6,802)
Ending balance, attributable to parent, tax	1,632		1,632		1,632
Ending balance, attributable to parent	(5,170)		(5,170)		(5,170)
Southwest Gas Corporation \| AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(46,540)	(53,310)	(49,049)	(47,073)	(51,779)
Beginning balance, attributable to parent			(49,049)
Ending balance, attributable to parent	(45,287)		(45,287)		(45,287)
Ending balance	$ (45,287)	$ (51,779)	$ (45,287)	$ (51,779)	$ (45,287)	$ (51,779)

Other Comprehensive Income and Accumulated Other Comprehensive Income - Amounts Recognized Before Tax, Defined Benefit Plans (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Equity [Abstract]
Net actuarial (loss) gain	$ (417,832)	$ (435,364)
Prior service cost	(2,080)	(3,033)
Less: amount recognized in regulatory assets	367,127	383,170
Recognized in AOCI	$ (52,785)	$ (55,227)

Segment Information - Additional Information (Detail)	9 Months Ended
Segment Information - Additional Information (Detail)	Sep. 30, 2019 Segment
Segment Reporting [Abstract]
Number of segments	2

Segment Information - Schedule of Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 725,230	$ 668,146	$ 2,271,780	$ 2,093,359	$ 3,058,434	$ 2,833,792
Segment net income (loss)	5,353	12,331	122,218	112,973	191,522	209,438
Operating Segments
Segment Reporting Information [Line Items]
Revenues	690,876	631,698	2,149,671	1,996,681	2,897,089	2,712,418
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	34,354	36,448	122,109	96,678	161,345	121,374
Segment Reconciling Items
Segment Reporting Information [Line Items]
Revenues	0	0	0	0	0	0
Segment net income (loss)	(473)	(797)	(1,253)	(1,362)	(1,433)	(1,922)
Natural Gas Operations
Segment Reporting Information [Line Items]
Revenues	209,980	217,523	989,368	987,515	1,359,581	1,354,000
Segment net income (loss)	(20,012)	(13,670)	86,746	79,301	146,287	153,683
Natural Gas Operations \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	209,980	217,523	989,368	987,515	1,359,581	1,354,000
Natural Gas Operations \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0	0	0
Utility Infrastructure Services
Segment Reporting Information [Line Items]
Revenues	515,250	450,623	1,282,412	1,105,844	1,698,853	1,479,792
Segment net income (loss)	25,838	26,798	36,725	35,034	46,668	57,677
Utility Infrastructure Services \| Operating Segments
Segment Reporting Information [Line Items]
Revenues	480,896	414,175	1,160,303	1,009,166	1,537,508	1,358,418
Utility Infrastructure Services \| Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	$ 34,354	$ 36,448	$ 122,109	$ 96,678	$ 161,345	$ 121,374

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Redeemable Noncontrolling Interests - Additional Information (Detail)	Sep. 30, 2019	Nov. 30, 2018
Noncontrolling Interest [Line Items]
Percentage of interest retained by noncontrolling party subject to election	100.00%
Linetec
Noncontrolling Interest [Line Items]
Ownership percentage by noncontrolling owners		20.00%

Redeemable Noncontrolling Interests - Summary of Redeemable Noncontrolling Interest (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Movement In Redeemable Noncontrolling Interest [Roll Forward]
Balance, December 31, 2018	$ 81,831
Net income attributable to redeemable noncontrolling interest	2,523
Balance, September 30, 2019	$ 84,354

Business Acquisitions - Narrative (Detail) - USD ($)		3 Months Ended	9 Months Ended	10 Months Ended	12 Months Ended
Business Acquisitions - Narrative (Detail) - USD ($)	Nov. 30, 2018	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Linetec
Business Acquisition [Line Items]
Ownership percentage by noncontrolling owners	20.00%
Linetec
Business Acquisition [Line Items]
Acquisition costs		$ 0	$ 0		$ 6,900,000
Centuri \| Linetec
Business Acquisition [Line Items]
Percentage of voting interests acquired	80.00%
Reduction to purchase price				$ 25,200,000
Payments to acquisition			$ 19,500,000
Remaining unpaid consideration	$ 26,200,000

Business Acquisitions - Summary of Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	10 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Nov. 30, 2018
Fair Values of Assets Acquired and Liabilities Assumed
Goodwill	$ 339,948	$ 359,045
Linetec
Fair Values of Assets Acquired and Liabilities Assumed
Cash and cash equivalents	3,900		$ 3,900
Accounts receivable	32,300		32,800
Revenue earned on contracts in progress in excess of billings	21,400		21,600
Prepaid expenses and other current assets	1,200		1,100
Property and equipment	88,600		89,400
Intangible assets	89,300		89,300
Goodwill	166,300		188,500
Total assets acquired	403,000		426,600
Accounts payable	8,000		8,000
Accrued liabilities	8,500		6,900
Deferred compensation and related accrued taxes	3,400		3,400
Redeemable noncontrolling interest	81,700		81,700
Total liabilities assumed and noncontrolling interest	101,600		100,000
Net assets acquired	301,400		$ 326,600
Measurement Period Adjustments
Accounts receivable, measurement period adjustments	(500)
Revenue earned on contracts in progress in excess of billings, measurement period adjustments	(200)
Prepaid expenses and other current assets, measurement period adjustments	100
Property and equipment, measurement period adjustments	(800)
Intangible assets, measurement period adjustments	0
Goodwill, measurement period adjustments	(22,200)
Total assets acquired, measurement period adjustments	(23,600)
Accrued liabilities, measurement period adjustments	1,600
Total liabilities assumed and noncontrolling interest, measurement period adjustments	1,600
Net assets acquired, measurement period adjustments	$ (25,200)