0001692115-21-000048 | 10-Q | XBRL Viewer | Southwest GAS Holdings INC

Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2021	Oct. 29, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
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	8360 S. Durango Drive
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
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		60,385,084
Entity Central Index Key	0001692115
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Southwest Gas Holdings, Inc. Common Stock, $1 Par Value
Entity Information [Line Items]
Title of 12(b) Security	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value
Trading Symbol	SWX
Security Exchange Name	NYSE
Preferred Stock Purchase Rights
Entity Information [Line Items]
Title of 12(b) Security	Preferred Stock Purchase Rights
No Trading Symbol Flag	true
Security Exchange Name	NYSE
Southwest Gas Corporation
Entity Information [Line Items]
Document Type	10-Q
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	8360 S. Durango Drive
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
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0000092416
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Utility plant:
Gas plant	$ 8,742,806	$ 8,384,000
Less: accumulated depreciation	(2,499,488)	(2,419,348)
Construction work in progress	153,100	211,429
Net utility plant	6,396,418	6,176,081
Other property and investments	1,305,334	834,245
Current assets:
Cash and cash equivalents	186,690	83,352
Accounts receivable, net of allowances	692,135	522,172
Accrued utility revenue	39,700	82,400
Income taxes receivable, net	32,554	10,884
Deferred purchased gas costs	240,827	2,053
Prepaid and other current assets	200,700	170,152
Total current assets	1,392,606	871,013
Noncurrent assets:
Goodwill	791,902	345,184
Deferred income taxes	268	455
Deferred charges and other assets	483,107	508,875
Total noncurrent assets	1,275,277	854,514
Total assets	10,369,635	8,735,853
Capitalization:
Common stock	62,009	58,823
Additional paid-in capital	1,823,889	1,609,155
Accumulated other comprehensive loss, net	(55,951)	(61,003)
Retained earnings	1,079,869	1,067,978
Total equity	2,909,816	2,674,953
Redeemable noncontrolling interest	183,547	165,716
Long-term debt, less current maturities	3,573,783	2,732,200
Total capitalization	6,667,146	5,572,869
Current liabilities:
Current maturities of long-term debt	297,271	40,433
Short-term debt	272,000	107,000
Accounts payable	222,959	231,301
Customer deposits	51,816	67,920
Income taxes payable, net	27,490	12,556
Accrued general taxes	60,656	48,640
Accrued interest	38,600	20,536
Deferred purchased gas costs	0	54,636
Other current liabilities	384,442	328,945
Total current liabilities	1,355,234	911,967
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits, net	789,141	647,453
Accumulated removal costs	419,000	404,000
Other deferred credits and other long-term liabilities	1,139,114	1,199,564
Total deferred income taxes and other credits	2,347,255	2,251,017
Total capitalization and liabilities	10,369,635	8,735,853
Southwest Gas Corporation
Utility plant:
Gas plant	8,742,806	8,384,000
Less: accumulated depreciation	(2,499,488)	(2,419,348)
Construction work in progress	153,100	211,429
Net utility plant	6,396,418	6,176,081
Other property and investments	149,926	143,611
Current assets:
Cash and cash equivalents	122,758	41,070
Accounts receivable, net of allowances	103,430	146,861
Accrued utility revenue	39,700	82,400
Income taxes receivable, net	17,775	11,155
Deferred purchased gas costs	240,827	2,053
Prepaid and other current assets	170,470	152,748
Total current assets	694,960	436,287
Noncurrent assets:
Goodwill	10,095	10,095
Deferred charges and other assets	461,212	490,562
Total noncurrent assets	471,307	500,657
Total assets	7,712,611	7,256,636
Capitalization:
Common stock	49,112	49,112
Additional paid-in capital	1,617,796	1,410,345
Accumulated other comprehensive loss, net	(55,759)	(61,135)
Retained earnings	851,645	835,146
Total equity	2,462,794	2,233,468
Long-term debt, less current maturities	2,309,857	2,438,206
Total capitalization	4,772,651	4,671,674
Current liabilities:
Current maturities of long-term debt	275,000	0
Short-term debt	250,000	57,000
Accounts payable	113,810	161,646
Customer deposits	51,816	67,920
Accrued general taxes	60,656	48,640
Accrued interest	34,938	20,495
Deferred purchased gas costs	0	54,636
Payable to parent	207	142
Other current liabilities	155,490	146,046
Total current liabilities	941,917	556,525
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits, net	618,597	581,100
Accumulated removal costs	419,000	404,000
Other deferred credits and other long-term liabilities	960,446	1,043,337
Total deferred income taxes and other credits	1,998,043	2,028,437
Total capitalization and liabilities	$ 7,712,611	$ 7,256,636

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Common stock, par (in USD per share)	$ 1	$ 1
Common stock, authorized (in shares)	120,000,000	120,000,000
Common stock, issued (in shares)	60,378,684	57,192,925
Common stock, outstanding (in shares)	60,378,684	57,192,925

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenues:
Gas operating revenues	$ 255,848	$ 210,834	$ 1,070,576	$ 976,095	$ 1,445,066	$ 1,355,666
Utility infrastructure services revenues	632,848	580,392	1,525,448	1,408,698	2,065,038	1,877,264
Total operating revenues	888,696	791,226	2,596,024	2,384,793	3,510,104	3,232,930
Operating expenses:
Net cost of gas sold	63,710	36,321	296,227	264,615	374,449	356,925
Operations and maintenance	122,927	101,764	334,450	304,964	437,602	407,924
Depreciation and amortization	91,380	80,139	267,670	245,009	354,688	324,995
Taxes other than income taxes	20,109	15,787	60,134	47,507	76,087	63,195
Utility infrastructure services expenses	567,270	502,951	1,381,524	1,252,489	1,858,464	1,671,478
Total operating expenses	865,396	736,962	2,340,005	2,114,584	3,101,290	2,824,517
Operating income (loss)	23,300	54,264	256,019	270,209	408,814	408,413
Other income and (expenses):
Net interest deductions	(31,298)	(28,311)	(81,201)	(83,141)	(109,537)	(111,705)
Other income (deductions)	(3,112)	1,799	(3,975)	(11,046)	282	(7,788)
Total other income and (expenses)	(34,410)	(26,512)	(85,176)	(94,187)	(109,255)	(119,493)
Income (loss) before income taxes	(11,110)	27,752	170,843	176,022	299,559	288,920
Income tax expense (benefit)	(1,816)	6,689	34,818	42,073	58,498	63,065
Net income (loss)	(9,294)	21,063	136,025	133,949	241,061	225,855
Net income attributable to noncontrolling interest	2,282	2,790	5,189	5,169	6,681	5,357
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (11,576)	$ 18,273	$ 130,836	$ 128,780	$ 234,380	$ 220,498
Earnings (loss) per share:
Basic (in USD per share)	$ (0.19)	$ 0.32	$ 2.23	$ 2.31	$ 4.03	$ 3.97
Diluted (in USD per share)	$ (0.19)	$ 0.32	$ 2.23	$ 2.31	$ 4.02	$ 3.97
Weighted average shares:
Basic (in shares)	59,688	56,271	58,639	55,683	58,209	55,508
Diluted (in shares)	59,816	56,357	58,742	55,753	58,312	55,577
Southwest Gas Corporation
Operating revenues:
Gas operating revenues	$ 255,848	$ 210,834	$ 1,070,576	$ 976,095	$ 1,445,066	$ 1,355,666
Operating expenses:
Net cost of gas sold	63,710	36,321	296,227	264,615	374,449	356,925
Operations and maintenance	119,708	101,159	328,980	303,567	431,795	406,169
Depreciation and amortization	61,359	55,942	187,688	173,865	249,118	230,158
Taxes other than income taxes	20,109	15,787	60,134	47,507	76,087	63,195
Total operating expenses	264,886	209,209	873,029	789,554	1,131,449	1,056,447
Operating income (loss)	(9,038)	1,625	197,547	186,541	313,617	299,219
Other income and (expenses):
Net interest deductions	(24,922)	(26,103)	(71,263)	(75,152)	(97,259)	(100,115)
Other income (deductions)	(4,287)	1,751	(4,902)	(10,947)	(545)	(7,615)
Total other income and (expenses)	(29,209)	(24,352)	(76,165)	(86,099)	(97,804)	(107,730)
Income (loss) before income taxes	(38,247)	(22,727)	121,382	100,442	215,813	191,489
Income tax expense (benefit)	(10,703)	(6,754)	18,798	20,874	33,679	35,496
Net income (loss)	(27,544)	(15,973)	$ 102,584	$ 79,568	182,134	155,993
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (27,544)	$ (15,973)			$ 182,134	$ 155,993

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net income	$ (9,294)	$ 21,063	$ 136,025	$ 133,949	$ 241,061	$ 225,855
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(43,730)	(54,026)
Amortization of prior service cost	183	220	547	659	766	901
Amortization of net actuarial loss	8,474	7,187	25,420	21,563	32,608	26,004
Prior service cost	0	0	0	0	0	(1,426)
Regulatory adjustment	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Net defined benefit pension plans	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income (loss)	413	783	1,240	2,054	1,653	2,689
Net forward-starting interest rate swaps	413	783	1,240	2,054	1,653	2,689
Foreign currency translation adjustments	(2,056)	1,024	(324)	(1,187)	2,576	(280)
Total other comprehensive income (loss), net of tax	(263)	2,834	5,052	3,949	(3,168)	(5,008)
Comprehensive income (loss)	(9,557)	23,897	141,077	137,898	237,893	220,847
Comprehensive income attributable to noncontrolling interest	2,282	2,790	5,189	5,169	6,681	5,357
Comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	(11,839)	21,107	135,888	132,729	231,212	215,490
Southwest Gas Corporation
Net income	(27,544)	(15,973)	102,584	79,568	182,134	155,993
Defined benefit pension plans:
Net actuarial loss	0	0	0	0	(43,730)	(54,026)
Amortization of prior service cost	183	220	547	659	766	901
Amortization of net actuarial loss	8,474	7,187	25,420	21,563	32,608	26,004
Prior service cost	0	0	0	0	0	(1,426)
Regulatory adjustment	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Net defined benefit pension plans	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Forward-starting interest rate swaps (“FSIRS”):
Amounts reclassified into net income (loss)	413	783	1,240	2,054	1,653	2,689
Net forward-starting interest rate swaps	413	783	1,240	2,054	1,653	2,689
Total other comprehensive income (loss), net of tax	1,793	1,810	5,376	5,136	(5,744)	(4,728)
Comprehensive income (loss)	$ (25,751)	$ (14,163)	$ 107,960	$ 84,704	$ 176,390	$ 151,265

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 136,025	$ 133,949	$ 241,061	$ 225,855
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	267,670	245,009	354,688	324,995
Deferred income taxes	45,374	37,752	58,339	45,815
Changes in current assets and liabilities:
Accounts receivable, net of allowances	(62,081)	(42,139)	(68,714)	(76,769)
Accrued utility revenue	42,700	42,600	(3,200)	(700)
Deferred purchased gas costs	(293,410)	59,899	(317,070)	38,016
Accounts payable	(51,086)	(59,031)	251	(14,817)
Accrued taxes	5,954	17,991	3,134	26,075
Other current assets and liabilities	23,289	121,185	9,531	121,274
Gains on sale of equipment	(5,365)	(581)	(6,632)	(2,897)
Changes in undistributed stock compensation	7,676	5,789	9,001	6,618
Equity AFUDC	0	(3,413)	(1,311)	(4,395)
Changes in deferred charges and other assets	(7,956)	(19,174)	(21,373)	(24,370)
Changes in other liabilities and deferred credits	(57,269)	(52,018)	(67,922)	(54,996)
Net cash provided by operating activities	51,521	487,818	189,783	609,704
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(506,737)	(632,474)	(699,368)	(851,236)
Acquisition of businesses, net of cash acquired	(830,395)	(250)	(830,145)	(28,355)
Changes in customer advances	7,940	7,691	14,282	11,643
Other	14,755	6,520	17,238	8,811
Net cash used in investing activities	(1,314,437)	(618,513)	(1,497,993)	(859,137)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	210,812	90,635	259,422	119,240
Dividends paid	(102,292)	(93,317)	(134,479)	(123,099)
Issuance of long-term debt, net	1,654,960	650,619	1,666,718	699,601
Retirement of long-term debt	(406,815)	(289,295)	(473,926)	(375,909)
Change in credit facility and commercial paper	(150,000)	(92,000)	(58,000)	(92,000)
Change in short-term debt	165,000	(157,000)	218,000	24,000
Withholding remittance - share-based compensation	(1,254)	(2,736)	(1,254)	(2,736)
Other	(4,355)	(1,596)	(6,161)	(4,090)
Net cash provided by financing activities	1,366,056	105,310	1,470,320	245,007
Effects of currency translation on cash and cash equivalents	198	(209)	635	(109)
Change in cash and cash equivalents	103,338	(25,594)	162,745	(4,535)
Cash and cash equivalents at beginning of period	83,352	49,539	23,945	28,480
Cash and cash equivalents at end of period	186,690	23,945	186,690	23,945
SUPPLEMENTAL INFORMATION:
Interest paid, net of amounts capitalized	57,128	63,743	98,567	103,836
Income taxes paid (received), net	7,665	(16,006)	12,720	(13,625)
Southwest Gas Corporation
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	102,584	79,568	182,134	155,993
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	187,688	173,865	249,118	230,158
Deferred income taxes	35,800	25,633	55,164	23,415
Changes in current assets and liabilities:
Accounts receivable, net of allowances	43,430	70,129	(22,766)	(7,135)
Accrued utility revenue	42,700	42,600	(3,200)	(700)
Deferred purchased gas costs	(293,410)	59,899	(317,070)	38,016
Accounts payable	(42,536)	(50,314)	17,396	(476)
Accrued taxes	5,396	15,914	(12,045)	29,228
Other current assets and liabilities	18,608	74,892	(7,739)	76,194
Changes in undistributed stock compensation	5,437	4,492	6,239	4,928
Equity AFUDC	0	(3,413)	(1,311)	(4,395)
Changes in deferred charges and other assets	(18,726)	(27,688)	(35,329)	(38,357)
Changes in other liabilities and deferred credits	(55,905)	(52,532)	(68,509)	(55,536)
Net cash provided by operating activities	31,066	413,045	42,082	451,333
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(415,398)	(525,221)	(582,393)	(716,564)
Changes in customer advances	7,940	7,691	14,282	11,643
Other	65	183	653	139
Net cash used in investing activities	(407,393)	(517,347)	(567,458)	(704,782)
CASH FLOW FROM FINANCING ACTIVITIES:
Contributions from parent	202,583	131,961	248,544	165,711
Dividends paid	(82,000)	(77,500)	(109,000)	(102,400)
Issuance of long-term debt, net	297,318	446,508	297,318	446,508
Retirement of long-term debt	0	(125,000)	0	(125,000)
Change in credit facility and commercial paper	(150,000)	(92,000)	(58,000)	(92,000)
Change in short-term debt	193,000	(194,000)	250,000	(30,000)
Withholding remittance - share-based compensation	(1,254)	(2,736)	(1,254)	(2,737)
Other	(1,632)	(1,186)	(1,708)	(1,210)
Net cash provided by financing activities	458,015	86,047	625,900	258,872
Change in cash and cash equivalents	81,688	(18,255)	100,524	5,423
Cash and cash equivalents at beginning of period	41,070	40,489	22,234	16,811
Cash and cash equivalents at end of period	122,758	22,234	122,758	22,234
SUPPLEMENTAL INFORMATION:
Interest paid, net of amounts capitalized	53,220	57,168	92,778	94,106
Income taxes paid (received), net	$ 0	$ (22,962)	$ 3,359	$ (22,262)

CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Southwest Gas Corporation	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value Southwest Gas Corporation	Additional paid-in capital	Additional paid-in capital Southwest Gas Corporation	Accumulated other comprehensive loss	Accumulated other comprehensive loss Southwest Gas Corporation	Retained earnings	Retained earnings Southwest Gas Corporation	Southwest Gas Holdings, Inc.
Beginning balance (in shares) at Dec. 31, 2019			55,007,000
Beginning balance at Dec. 31, 2019			$ 56,637		$ 1,466,937	$ 1,229,083	$ (56,732)	$ (55,151)	$ 1,039,072	$ 782,108
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,452,000
Common stock issuances			$ 1,452		92,877
Foreign currency exchange translation adjustment							(1,187)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							3,082	3,082
FSIRS amounts reclassified to net income, net of tax	$ 2,054	$ 2,054					2,054	2,054
Net income (loss)									128,780	79,568
Share-based compensation						2,397				(641)
Contributions from Southwest Gas Holdings, Inc.						131,961
Dividends declared									(96,161)	(79,300)
Redemption value adjustments									(17,573)
Ending balance (in shares) at Sep. 30, 2020			56,459,000	47,482,000
Ending balance at Sep. 30, 2020		2,144,273	$ 58,089	$ 49,112	1,559,814	1,363,441	(52,783)	(50,015)	1,054,118	781,735	$ 2,619,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.71
Beginning balance (in shares) at Jun. 30, 2020			55,910,000
Beginning balance at Jun. 30, 2020			$ 57,540		1,523,630	1,329,843	(55,617)	(51,825)	1,085,742	824,847
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			549,000
Common stock issuances			$ 549		36,184
Foreign currency exchange translation adjustment							1,024
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							1,027	1,027
FSIRS amounts reclassified to net income, net of tax	$ 783	783					783	783
Net income (loss)									18,273	(15,973)
Share-based compensation						1,137				(139)
Contributions from Southwest Gas Holdings, Inc.						32,461
Dividends declared									(32,324)	(27,000)
Redemption value adjustments									(17,573)
Ending balance (in shares) at Sep. 30, 2020			56,459,000	47,482,000
Ending balance at Sep. 30, 2020		2,144,273	$ 58,089	$ 49,112	1,559,814	1,363,441	(52,783)	(50,015)	1,054,118	781,735	2,619,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.57
FSIRS amounts reclassified to net income, net of tax	$ 1,653	1,653
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		2,462,794	$ 62,009	$ 49,112	1,823,889	1,617,796	(55,951)	(55,759)	1,079,869	851,645	2,909,816
Beginning balance (in shares) at Dec. 31, 2020	57,192,925		57,193,000
Beginning balance at Dec. 31, 2020			$ 58,823		1,609,155	1,410,345	(61,003)	(61,135)	1,067,978	835,146
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			3,186,000
Common stock issuances			$ 3,186		214,734
Foreign currency exchange translation adjustment							(324)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							4,136	4,136
FSIRS amounts reclassified to net income, net of tax	$ 1,240	1,240					1,240	1,240
Net income (loss)									130,836	102,584
Share-based compensation						4,868				(685)
Contributions from Southwest Gas Holdings, Inc.						202,583
Dividends declared									(106,303)	(85,400)
Redemption value adjustments	$ 12,642								(12,642)
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		2,462,794	$ 62,009	$ 49,112	1,823,889	1,617,796	(55,951)	(55,759)	1,079,869	851,645	2,909,816
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.785
Beginning balance (in shares) at Jun. 30, 2021			59,088,000
Beginning balance at Jun. 30, 2021			$ 60,718		1,733,572	1,529,419	(55,688)	(57,552)	1,108,279	908,757
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,291,000
Common stock issuances			$ 1,291		90,317
Foreign currency exchange translation adjustment							(2,056)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							1,380	1,380
FSIRS amounts reclassified to net income, net of tax	$ 413	413					413	413
Net income (loss)									(11,576)	(27,544)
Share-based compensation						1,435				(168)
Contributions from Southwest Gas Holdings, Inc.						86,942
Dividends declared									(36,098)	(29,400)
Redemption value adjustments									19,264
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		$ 2,462,794	$ 62,009	$ 49,112	$ 1,823,889	$ 1,617,796	$ (55,951)	$ (55,759)	$ 1,079,869	$ 851,645	$ 2,909,816
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.595

Background, Organization, and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

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).

In October 2021, Southwest Gas Holdings, Inc. (the “Company”) entered into an agreement with Dominion Energy Questar Corporation, a wholly owned subsidiary of Dominion Energy, Inc., to acquire all equity interests in Dominion Energy Questar Pipeline, LLC and related entities (“Questar Pipelines”). Upon closing, Questar Pipelines will operate as part of a standalone subsidiary of the Company, and will undergo new branding at or subsequent to close. The agreement provides for consideration of $1.545 billion in cash (subject to certain adjustments) and assumption of approximately $430 million of existing long-term debt. The agreement contains certain termination rights, including a mutual termination right exercisable at any time and a unilateral termination right exercisable by either party if certain conditions have not been met by December 31, 2021 (the initial termination date), subject to an extension unilaterally exercisable by either party if certain conditions have not been met, subsequently extending the initial termination date through June 30, 2022. The completion of this transaction is subject to closing conditions, including the expiration or termination of any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, and approval of certain aspects of the transaction by the Federal Communications Commission. The operations to be acquired would further diversify the Company’s business with an expansion of regulated interstate natural gas pipelines and underground storage services as part of the jurisdiction of the Federal Energy Regulatory Commission (the “FERC”), thereby expanding transportation services into Utah, Wyoming, and Colorado. The Company plans to initially fund this acquisition with a new 364-day term loan, followed by permanent financing. See Note 5 – Debt for more information.

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 primarily from installation, replacement, repair, and maintenance of energy distribution systems. 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”), Linetec Services, LLC (“Linetec”), and Riggs Distler & Company, Inc. (“Riggs Distler”). 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. Centuri completed the acquisition of Drum Parent, Inc. (“Drum”), including Drum’s most significant operating subsidiary, Riggs Distler, in August 2021, thereby expanding Centuri’s electric services footprint in the Northeast and Mid-Atlantic regions of the U.S. See Note 8 - Business Acquisitions for more information.

Basis of Presentation. The condensed consolidated financial statements of Southwest Gas Holdings, Inc. and subsidiaries 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.

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 as of 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. In association with the novel Coronavirus (“COVID-19”) pandemic environment, utility operations, and to a large extent, utility infrastructure services, were deemed “essential services.” Management has considered the impact of the pandemic and adjusted certain estimates, where relevant, in the preparation of the condensed consolidated financial statements.

These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the 2020 Annual Report to Stockholders, which is incorporated by reference into the 2020 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, 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, 2021		December 31, 2020
Southwest Gas Corporation:
Net cash surrender value of COLI policies	$	147,187	$	140,874
Other property	2,739		2,737
Total Southwest Gas Corporation	149,926		143,611
Centuri property, equipment, and intangibles	1,592,461		1,089,414
Centuri accumulated provision for depreciation and amortization	(468,206)		(422,741)
Other property and investments	31,153		23,961
Total Southwest Gas Holdings, Inc.	$	1,305,334	$	834,245

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. Balances reflect impacts of equity and fixed-income securities underlying the cash surrender values at each reporting date; however, ultimately, only the insurance proceeds are ever actually received, due to management’s intent to hold the policies to maturity.

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 of the Company include $55 million of money market fund investments at September 30, 2021, and an insignificant amount at December 31, 2020. The money market fund investments for Southwest were insignificant at both balance sheet dates. These investments 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 include customer advances applied as contributions toward utility construction activity, and capital expenditures that were not yet paid as of period-end reporting dates, but rather were included in accounts payable. Typical activities that represent aspects of both non-cash investing and non-cash financing activities relate to right-of-use assets obtained in exchange for lease liabilities (including, at times, lease terminations and modifications). Amounts related to these collective activities were immaterial for the periods presented herein. See also Prepaid and other current assets below.

Intercompany Transactions. Centuri recognizes revenues generated from contracts with Southwest (see Note 7 – Segment Information). 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.

Accounts Receivable, net of allowances. Business activity with respect to natural gas utility operations is conducted with customers located within the three-state region of Arizona, Nevada, and California. Southwest’s accounts receivable are short-term in nature with no billing due dates customarily extending beyond one month, with customers’ credit worthiness assessed upon account creation by evaluation of other utility service and related payment history. Southwest lifted the moratorium on disconnection of natural gas service for non-payment in Arizona and Nevada in September 2021, which was initiated (at the same time as a moratorium on late fees) in March 2020 in response to the COVID-19 pandemic. The moratorium on disconnection continues to be in place for California, and is expected to be lifted in the fourth quarter of 2021. Southwest recommenced assessing late fees on past-due balances in Arizona and Nevada in April 2021, and expects to recommence late fees in California in the fourth quarter of 2021. Southwest is actively working with customers experiencing financial hardship by means of flexible payment options. Management continues to monitor expected credit losses in light of the impact of COVID-19. The allowance for uncollectible accounts receivable balances as of September 30, 2021 reflects the expected impact from the pandemic on balances as of that date, including consideration of customers’ ability to pay those amounts that are due.

Utility infrastructure services contracts receivable are recorded at face amounts less an allowance for doubtful accounts. Centuri’s customers are generally investment-grade gas and electric utility companies for which Centuri has historically recognized an insignificant amount of write-offs. Centuri has not been significantly impacted, nor does it anticipate it will experience significant difficulty in collecting amounts due, as a result of the current environment surrounding COVID-19 given the nature of its customers.

Activity between periods in the allowance for uncollectible accounts and the balances as of the periods presented within the Company’s and Southwest’s financial statements were not material to the condensed consolidated financial statements overall.

Deferred Purchased Gas Costs. The various regulatory commissions have established procedures to enable Southwest to adjust its billing rates for changes in the cost of natural gas purchased. The difference between the current cost of gas purchased and the cost of gas recovered in billed rates is deferred. Generally, these deferred amounts are recovered or refunded within one year.

In mid-February 2021, the central U.S. (from south Texas to North Dakota and the eastern Rocky Mountains) experienced extreme cold temperatures, which increased natural gas demand and caused supply issues due to wellhead freeze-offs, power outages, or other adverse operating conditions upstream of Southwest’s distribution systems. These conditions caused daily natural gas prices to reach unprecedented levels. During this time, Southwest secured natural gas supplies, albeit at substantially higher prices, maintaining service to its customers. The incremental cost for these supplies was approximately $250 million, funded using a 364-day $250 million term loan executed in March 2021 (see Note 5 – Debt). The incremental gas costs are expected to continue to be collected from customers through the purchased gas adjustment (“PGA”) mechanisms.

Following the extreme weather event, an interstate transmission pipeline company billed Southwest, in addition to customary transmission costs, $65 million (later reduced to approximately $55 million) for pipeline imbalance charges, allegedly incurred during the period of the pipeline’s critical operation condition. However, Southwest formally disputed the imbalance charges, in addition to interest on that amount, believing that no amounts were due to the pipeline. In June 2021, the interstate transmission pipeline company requested approval from the Federal Energy Regulatory Commission (the “FERC”) to waive these imbalance charges and interest, affirming that they had the authority to elect the option to waive the underlying charges based on their tariff, but were seeking approval by the FERC for purposes of transparency and regulatory certainty. In August 2021, FERC approval was received. Consequently, no amounts were recognized by Southwest related to the original charge from the pipeline.

Prepaid and other current assets. Prepaid and other current assets includes gas pipe materials and operating supplies of $55 million at September 30, 2021 and $50 million at December 31, 2020 (carried at weighted average cost).

In the third quarter of 2021, the Company and Southwest classified certain assets associated with its previous corporate headquarters as held for sale. As a result, the Company and Southwest reclassified approximately $31 million from Net utility plant to Prepaid and other current assets on their respective Condensed Consolidated Balance Sheets during the third quarter of 2021; this was a non-cash item and therefore did not impact the Company’s or Southwest’s respective Condensed Consolidated Statements of Cash Flows.

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 they remained consistent between periods presented below, and that no change was necessary with regard to the level at which goodwill is assessed for impairment. Since December 31, 2020, management also qualitatively assessed whether events during the first nine months of 2021 may have resulted in conditions whereby the carrying value of goodwill was higher than its fair value, which if the case, could be an indication of a permanent

impairment. Through this assessment, no such condition was believed to have existed and therefore, no impairment was deemed to have occurred. The Riggs Distler acquisition in August 2021 (see further discussion in Note 8 - Business Acquisitions) was deemed a stock purchase for tax purposes, and as a result, only pre-acquisition goodwill that was historically tax-deductible by Riggs Distler will continue to be deductible for tax purposes by the Company. Goodwill on Southwest’s and the Company’s Condensed Consolidated Balance Sheets includes:


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Total Company
December 31, 2020	$	10,095	$	335,089	$	345,184
Additional goodwill from Riggs Distler acquisition	—		446,794		446,794
Foreign currency translation adjustment	—		(76)		(76)
September 30, 2021	$	10,095	$	781,807	$	791,902

Other Current Liabilities. Management recognizes in its balance sheets various liabilities that are expected to be settled through future cash payment within the next twelve months, including amounts payable under regulatory mechanisms, customary accrued expenses for employee compensation and benefits, declared but unpaid dividends, and miscellaneous other accrued liabilities. Other current liabilities for the Company includes $35.9 million and $32.6 million of dividends declared as of September 30, 2021 and December 31, 2020, respectively, as well as liabilities included as part of the Riggs Distler acquisition.

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


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	—	$	4,500	$	5,800	$	1,000	$	14,000	$	7,200
Interest income	1,365		1,412		3,312		3,214		4,113		4,630
Equity AFUDC	—		1,232		—		3,413		1,311		4,395
Other components of net periodic benefit cost	(3,506)		(5,005)		(10,516)		(15,016)		(15,522)		(18,780)
Miscellaneous income and (expense)	(2,146)		(388)		(3,498)		(3,558)		(4,447)		(5,060)
Southwest Gas Corporation - total other income (deductions)	(4,287)		1,751		(4,902)		(10,947)		(545)		(7,615)
Utility infrastructure services segment:

Foreign transaction gain (loss)	(7)		—		(19)		(16)		(19)		(16)
Miscellaneous income and (expense)	1,182		48		946		(91)		846		(194)
Centuri - total other income (deductions)	1,175		48		927		(107)		827		(210)
Corporate and administrative	—		—		—		8		—		37
Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	(3,112)	$	1,799	$	(3,975)	$	(11,046)	$	282	$	(7,788)

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 the discussion of Other Property and Investments above and to Note 2 – Components of Net Periodic Benefit Cost.

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.

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. Adjustment to the redemption value also impacts retained earnings, as reflected in the Company’s Condensed Consolidated Statement of Equity, but does not impact net income. The following depicts the change to the balance of the redeemable noncontrolling interest:


(Thousands of dollars):	Redeemable Noncontrolling Interest
Balance, December 31, 2020	$	165,716
Net income attributable to redeemable noncontrolling interest	5,189
Redemption value adjustment	12,642
Balance, September 30, 2021	$	183,547

Earnings Per Share. Basic earnings per share (“EPS”) in each period of this report were calculated by dividing net income attributable to Southwest Gas Holdings, Inc. by the weighted-average number of shares during those periods. Diluted EPS includes additional weighted-average common stock equivalents (performance shares and restricted stock units). Unless otherwise noted, the term “Earnings Per Share” refers to Basic EPS. A reconciliation of the denominator used in Basic and Diluted EPS calculations is shown in the following table:


	Three Months Ended September 30,		Nine Months Ended September 30,		Twelve Months Ended September 30,
(In thousands)	2021	2020	2021	2020	2021	2020
Weighted average basic shares	59,688	56,271	58,639	55,683	58,209	55,508
Effect of dilutive securities:
Management Incentive Plan shares	—	—	—	—	—	3
Restricted stock units (1)	128	86	103	70	103	66
Weighted average diluted shares	59,816	56,357	58,742	55,753	58,312	55,577

(1) The number of securities included 115,000 and 76,000 performance shares during the three months ending September 30, 2021 and 2020, 95,000 and 63,000 performance shares during the nine months ending September 30, 2021 and 2020, and 93,000 and 57,000 performance shares during the twelve months ending September 30, 2021 and 2020, respectively, the total of which was derived by assuming that target performance will be achieved during the relevant performance period.

Contingency. Southwest maintains liability insurance for various risks associated with the operation of its natural gas pipelines and facilities. In connection with these liability insurance policies, Southwest is responsible for an initial deductible or self-insured retention amount per incident, after which the insurance carriers would be responsible for amounts up to the policy limits. For the policy year August 2021 to July 2022, these liability insurance policies require Southwest to be responsible for the first $1 million (self-insured retention) of each incident plus the first $4 million in aggregate claims above its self-insured retention in the policy year. In August 2021, a natural gas pipe was involved in an explosion that injured four individuals and damaged property. The explosion was caused by a leak in the pipe, and is under investigation. Claims are expected to be filed against Southwest. If Southwest is deemed fully or partially responsible, Southwest estimates its exposure could be as much as $5 million (the maximum noted above). As of September 30, 2021, pursuant to Accounting Standards Codification 450, Contingencies, Southwest recorded a $5 million liability related to this incident reflecting the maximum noted above; an estimate of actual loss greater than this exposure (to be covered by insurance) cannot be estimated as of the date these financial statements are issued.

Recent Accounting Standards Updates.

Accounting pronouncements adopted in 2021:

In December 2019, the Financial Accounting Standards Board (the “FASB”) issued ASU 2019-12 “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” The update simplifies the accounting for income taxes by removing certain exceptions to the general principles, as well as improving consistent application in Topic 740 by clarifying and amending existing guidance. The Company and Southwest adopted the update in the first quarter of 2021, the impact of which was not material to the condensed consolidated financial statements of the Company or Southwest.

Recently issued accounting pronouncements that will be effective after 2021:

In March 2020, the FASB issued ASU 2020-04 “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” The update provides optional guidance for a limited time to ease the potential burden in accounting for, or recognizing the effects of, reference rate reform on financial reporting, including when modifying a contract (during the eligibility period covered by the update to Topic 848) to replace a reference rate affected by such reform. The update applies only to contracts and hedging relationships that reference the London Interbank Offered Rate (“LIBOR”) or another rate expected to be discontinued due to reference rate reform. The guidance was eligible to be applied upon issuance on March 12, 2020, and can generally be applied through December 31, 2022, but to date, no further updates have occurred that would extend the optional guidance to the full tenor of LIBOR expiration dates occurring after 2022. Management will monitor the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures, and will reflect such appropriately, in the event that the optional guidance is elected. It will also monitor further FASB action, if any, in regard to the full tenor of LIBOR expiration dates. See also LIBOR discussion in Note 5 – Debt.

In August 2020, the FASB issued ASU 2020-06 “Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity.” The update, amongst other amendments, improves the guidance related to the disclosures and earnings-per-share for convertible instruments and contracts in an entity’s own equity. The update is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years; early adoption is permitted. Management is evaluating what impacts, if any, this update might have on the Company’s consolidated financial statements and disclosures.

Components of Net Periodic Benefit Cost

9 Months Ended

Sep. 30, 2021

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 is a component of an overhead loading process associated with the cost of labor. The overhead process ultimately results in allocation of service cost 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
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	10,289	$	8,576	$	30,869	$	25,725	$	39,443	$	32,191
Interest cost	10,108		11,388		30,324		34,165		41,714		46,416
Expected return on plan assets	(18,088)		(16,324)		(54,264)		(48,972)		(70,588)		(64,033)
Amortization of net actuarial loss	10,489		9,006		31,467		27,019		40,473		32,608
Net periodic benefit cost	$	12,798	$	12,646	$	38,396	$	37,937	$	51,042	$	47,182

	SERP
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	131	$	97	$	394	$	292	$	491	$	359
Interest cost	358		401		1,074		1,204		1,474		1,644
Amortization of net actuarial loss	661		451		1,981		1,353		2,433		1,608
Net periodic benefit cost	$	1,150	$	949	$	3,449	$	2,849	$	4,398	$	3,611

	PBOP
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	423	$	395	$	1,269	$	1,186	$	1,664	$	1,505
Interest cost	549		646		1,645		1,936		2,291		2,697
Expected return on plan assets	(810)		(852)		(2,430)		(2,556)		(3,282)		(3,345)
Amortization of prior service costs	239		289		719		867		1,007		1,185

Net periodic benefit cost	$	401	$	478	$	1,203	$	1,433	$	1,680	$	2,042

For new employees hired on or after January 1, 2022, the defined benefit retirement plan will be replaced with enhanced contributions to the 401(k) plan. The change is not applicable to existing employees, nor to employees hired during the remainder of 2021. Current employees will continue to be eligible to receive employer 401(k) matching contributions on one-half of amounts deferred by them, up to a maximum matching contribution of 3.5% of their eligible annual compensation. Employees hired after 2021 will be eligible for enhanced employer 401(k) contributions of 3% plus a matching contribution (dollar-for-dollar) up to 7% of eligible compensation.

Revenue

9 Months Ended

Sep. 30, 2021

Revenue from Contract with Customer [Abstract]

Revenue

Note 3 – Revenue

The following information about the Company’s revenues is presented by segment. Southwest encompasses the natural gas operations segment and Centuri encompasses the utility infrastructure services segment.

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 September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Residential	$	147,326	$	131,008	$	743,791	$	690,861	$	1,011,450	$	957,379
Small commercial	48,283		35,204		185,774		159,122		248,193		228,720
Large commercial	14,199		9,942		40,030		32,588		52,075		45,493
Industrial/other	9,608		5,888		30,352		19,089		37,505		25,435
Transportation	21,884		21,040		68,217		65,281		91,151		89,364
Revenue from contracts with customers	241,300		203,082		1,068,164		966,941		1,440,374		1,346,391
Alternative revenue program revenues (deferrals)	12,569		9,199		(5,335)		9,545		(2,740)		7,629
Other revenues (1)	1,979		(1,447)		7,747		(391)		7,432		1,646
Total Gas operating revenues	$	255,848	$	210,834	$	1,070,576	$	976,095	$	1,445,066	$	1,355,666

(1) Amounts include late fees and other miscellaneous revenues, and may also include the impact of certain regulatory mechanisms, such as cost-of-service components in customer rates expected to be returned to customers in future periods. Also includes the impacts of a temporary moratorium on late fees and disconnection for nonpayment during the COVID-19 pandemic.

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:


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Service Types:
Gas infrastructure services	$	393,122	$	387,578	$	961,836	$	935,444	$	1,287,552	$	1,288,468
Electric power infrastructure services	155,456		115,386		347,061		282,992		475,895		346,432
Other	84,270		77,428		216,551		190,262		301,591		242,364
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Contract Types:
Master services agreement	$	467,869	$	437,914	$	1,160,199	$	1,076,961	$	1,573,247	$	1,438,540
Bid contract	164,979		142,478		365,249		331,737		491,791		438,724
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264

Unit price contracts	$	406,404	$	377,284	$	1,002,779	$	985,673	$	1,373,746	$	1,359,352
Fixed price contracts	64,632		46,379		149,681		109,935		197,447		142,356
Time and materials contracts	161,812		156,729		372,988		313,090		493,845		375,556
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264

The following table provides information about contracts receivable and revenue earned on contracts in progress in excess of billings (contract assets), which are both included within Accounts receivable, net of allowances; the table also includes amounts billed in excess of revenue earned on contracts (contract liabilities), which are included in Other current liabilities as of September 30, 2021 and December 31, 2020 on the Company’s Condensed Consolidated Balance Sheets:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Contracts receivable, net	$	381,387	$	278,316
Revenue earned on contracts in progress in excess of billings	207,318		96,996
Amounts billed in excess of revenue earned on contracts	19,954		4,507

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 for billing 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 relate 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, 2020 to September 30, 2021 is due to revenue recognized of approximately $4.5 million that was included in this item as of January 1, 2021, after which time it became earned and the balance was reduced; the change also includes 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. Furthermore, 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, 2021, Centuri had 18 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, 2021 was $53.8 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, 2021		December 31, 2020
Billed on completed contracts and contracts in progress	$	380,484	$	273,778
Other receivables	2,844		6,692
Contracts receivable, gross	383,328		280,470
Allowance for doubtful accounts	(1,941)		(2,154)
Contracts receivable, net	$	381,387	$	278,316

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-URI http://asc.fasb.org/topic&trid=49130388

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130551-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
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-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130558-203045

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045

+ Details

Common Stock

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Common Stock

Note 4 – Common Stock

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 April 8, 2021, the Company entered into a Sales Agency Agreement between the Company and BNY Mellon Capital Markets, LLC and J.P. Morgan Securities LLC (the “Equity Shelf Program”) for the offer and sale of up to $500 million of common stock from time to time in an at-the-market offering program. The shares are issued pursuant to the Company’s automatic shelf registration statement on Form S-3 (File No. 333-251074). The following table provides the activity under the Equity Shelf Program for the three-month and life-to-date periods ended September 30, 2021:


	Three Months Ended		Life-To-Date Ended
	September 30, 2021
Gross proceeds	$	87,819,931	$	158,180,343
Less: agent commissions	(878,199)		(1,581,803)
Net proceeds	$	86,941,732	$	156,598,540
Number of shares sold	1,251,810		2,302,407
Weighted average price per share	$	70.15	$	68.70

As of September 30, 2021, the Company had up to $341,819,657 in common stock available for sale under the program. Net proceeds from the sale 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, as well as for the repayment or repurchase of indebtedness (including amounts outstanding from time to time under the credit facilities, senior notes, term loan, or future credit facilities), and to provide for working capital.

During the quarter ended March 31, 2021, the Company sold essentially all of the remaining common stock available for sale under a previously effective equity shelf program.

During the nine months ended September 30, 2021, the Company issued approximately 47,500 shares of common stock through the Restricted Stock/Unit Plan and Omnibus Incentive Plan.

Additionally, during the nine months ended September 30, 2021, the Company issued 130,000 shares of common stock through the Dividend Reinvestment and Stock Purchase Plan, raising approximately $8.5 million.

On October 10, 2021, the Company’s Board of Directors (the “Board”) authorized and declared a dividend of one preferred stock purchase right (a “Right”) for each share of common stock outstanding, $1 par value per share, of the Company to stockholders of record at the close of business on October 21, 2021. Each right entitles the registered holder to purchase from the Company one ten-thousandth (a “unit”) of a share of Series A Junior Participating Preferred Stock, no par value per share, of the Company at a purchase price of $321.70 per unit, subject to adjustment. Generally, the Rights become exercisable in the event any person or group of affiliated or associated persons acquires beneficial ownership of 10% (20% in the case of a passive institutional investor) or more of the Company’s common stock without the approval of the Board, and until such time, are inseparable from and trade with the Company’s common stock. The Rights were issued pursuant to the Rights Agreement dated October 10, 2021 (the “Rights Agreement”), between the Company and Equiniti Trust Company, as rights agent. The Rights expire at the close of business on October 9, 2022 or upon an earlier merger or other acquisition transaction involving the Company, redemption, or exchange as provided in the Rights Agreement.

Debt

9 Months Ended

Sep. 30, 2021

Debt Disclosure [Abstract]

Debt

Note 5 – Debt

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. Details surrounding the fair value, as described in Note 1 – Background, Organization, and Summary of Significant Accounting Policies, and individual carrying values of instruments are provided in the table that follows.


	September 30, 2021				December 31, 2020
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 6.1%, due 2041	$	125,000	$	167,755	$	125,000	$	174,858
Notes, 3.875%, due 2022	250,000		252,208		250,000		258,825
Notes, 4.875%, due 2043	250,000		307,385		250,000		317,190
Notes, 3.8%, due 2046	300,000		326,058		300,000		347,046
Notes, 3.7%, due 2028	300,000		331,536		300,000		344,553
Notes, 4.15%, due 2049	300,000		343,950		300,000		370,278
Notes, 2.2%, due 2030	450,000		447,287		450,000		474,552
Notes, 3.18%, due 2051	300,000		291,351		—		—
8% Series, due 2026	75,000		94,752		75,000		99,723
Medium-term notes, 7.78% series, due 2022	25,000		25,513		25,000		26,663
Medium-term notes, 7.92% series, due 2027	25,000		31,936		25,000		33,802
Medium-term notes, 6.76% series, due 2027	7,500		9,116		7,500		9,613
Unamortized discount and debt issuance costs	(20,727)				(17,822)
	2,386,773				2,089,678
Revolving credit facility and commercial paper	—		—		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	(1,916)				(1,472)
	198,084				198,528
Less: current maturities	(275,000)				—
Long-term debt, less current maturities - Southwest Gas Corporation	$	2,309,857			$	2,438,206
Centuri:
Centuri term loan facility	$	1,145,000	$	1,146,431	$	226,648	$	230,824
Unamortized debt issuance costs	(25,385)				(820)
	1,119,615				225,828
Centuri secured revolving credit facility	112,236		112,348		26,626		26,645
Centuri other debt obligations	54,346		52,682		81,973		84,246
Less: current maturities	(22,271)				(40,433)
Long-term debt, less current maturities - Centuri	$	1,263,926			$	293,994
Consolidated Southwest Gas Holdings, Inc.:
Southwest Gas Corporation long-term debt	$	2,584,857			$	2,438,206
Centuri long-term debt	1,286,197				334,427
Less: current maturities	(297,271)				(40,433)
Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	3,573,783			$	2,732,200

The fair values of Southwest's and Centuri’s revolving credit facilities and Southwest’s IDRBs are categorized as Level 1 based on the FASB’s fair value hierarchy, due to the ability to access similar debt arrangements at measurement dates with comparable terms, including variable/market rates. The fair values of Southwest’s debentures (which include senior and medium-term notes) and Centuri's term loan facility as of September 30, 2021 were determined utilizing a market-based valuation approach, where fair values are determined based on evaluated pricing data, and as such are categorized as Level 2 in the hierarchy. Prior to amending its secured revolving credit and term loan facility in the third quarter 2021 (see below), the Centuri credit facility was categorized as Level 3, as fair values were based on a conventional discounted cash flow methodology utilizing current market pricing yield curves.

Southwest has a $400 million credit facility that is scheduled to expire in April 2025. Southwest designates $150 million of associated capacity as long-term debt and the remaining $250 million for working capital purposes. Interest rates for the credit facility are calculated at either 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, 2021, the applicable margin is 1.125% for loans bearing interest with reference to LIBOR and 0.125% for loans bearing interest with reference to the alternative base rate. At September 30, 2021, no borrowings were outstanding on the long-term portion (including under the commercial paper program, discussed below) of the facility or on the short-term portion of this credit facility discussed below.

Southwest has a $50 million commercial paper program. Issuances under the commercial paper program are supported by Southwest’s revolving credit facility and, therefore, do 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, 2021, as noted above, no borrowings were outstanding under the commercial paper program.

In August 2021, Southwest issued $300 million aggregate principal amount of 3.18% Senior Notes at a discount of 0.019%. The notes will mature in August 2051. Southwest used the net proceeds from the offering to repay the outstanding balance under its credit facility, with the remaining net proceeds used for general corporate purposes.

As referred to above, on August 27, 2021, Centuri, in association with the acquisition of Riggs Distler (see Note 8 - Business Acquisitions), entered into an amended and restated credit agreement. The agreement provided for a $1.145 billion secured term loan facility, at a discount of 1.00%, and a $400 million secured revolving credit facility, which in addition to funding the Riggs Distler acquisition, refinanced the previous $590 million loan facility. This multi-currency facility allows the borrower to request loan advances in either Canadian dollars or U.S. dollars. Amounts borrowed and repaid under the revolving line of credit portion of the facility are available to be re-borrowed. The obligations under the credit agreement are secured by present and future ownership interests in substantially all direct and indirect subsidiaries of Centuri, substantially all of the tangible and intangible personal property of each borrower, certain of their direct and indirect subsidiaries, and all products, profits, and proceeds of the foregoing. The term loan facility matures on August 27, 2028 and the revolving credit facility matures on August 27, 2026.

Interest rates for the term loan facility and the revolving credit facility are based on either a “base rate” or LIBOR, plus an applicable margin in either case. The term loan facility is also subject to a LIBOR floor of 0.50%. Furthermore, Centuri Canada Division Inc. may borrow under the revolving credit facility with interest rates based on either a “base rate” or the Canadian Dealer Offered Rate (“CDOR”) plus the applicable margin, at the borrower’s option. The margin for the term loan facility will be 1.50% for base rate loans and 2.50% for LIBOR loans. The margin for the revolving credit facility ranges from 0.0% to 1.25% for base rate loans and from 1.00% to 2.25% for LIBOR loans, depending on Centuri’s net leverage ratio. Upon the occurrence of certain events providing for a transition away from LIBOR, or if LIBOR is no longer a widely recognized benchmark rate, Centuri may further amend the credit agreement with a replacement rate as set forth in the amended agreement. Centuri is also required to pay a commitment fee on the unused portion of the commitments. The commitment fee ranges from 0.15% to 0.35% per annum. The credit agreement contains certain customary representations and warranties, affirmative and negative covenants and events of default. There are no financial covenants related to the term loan facility. The revolving credit facility requires Centuri to maintain a maximum total net leverage ratio of 5.50 to 1.00 with a step-down to 4.75 to 1.0 on December 31, 2022, and a step-down to 4.00 to 1.00 on December 31, 2023; provided, however, Centuri may elect to increase the maximum total net leverage ratio up to 4.50 to 1.00 in connection with certain material acquisitions, with such increase being applicable for one year following such acquisition; and the agreement also requires Centuri to maintain a minimum interest coverage ratio of 2.50 to 1.00. Centuri’s assets securing the facility at September 30, 2021 totaled $2.6 billion. At September 30, 2021, $1.257 billion in borrowings were outstanding under Centuri’s combined secured revolving credit and term loan facility.

Short-Term Debt

Southwest Gas Holdings, Inc. has a $100 million credit facility that is scheduled to expire in April 2025 and is primarily used for short-term financing needs. There was $22 million outstanding under this credit facility as of September 30, 2021.

As indicated above, under Southwest’s $400 million credit facility, no short-term borrowings were outstanding at September 30, 2021.

In March 2021, Southwest entered into a $250 million Term Loan that matures March 22, 2022. The proceeds were used to fund the increased cost of natural gas supply during the month of February 2021, caused by extreme weather conditions in the central U.S. (see Deferred Purchased Gas Costs in Note 1 – Background, Organization, and Summary of Significant Accounting Policies). Interest rates for the term loan are calculated at either LIBOR or an “alternate base rate,” plus in each case an applicable margin that is determined based on Southwest’s senior unsecured long-term debt rating. The applicable margin ranges from 0.550% to 1.000% for loans bearing interest with reference to LIBOR and 0.000% for loans bearing interest with reference to an alternate base rate. The agreement contains a financial covenant requiring Southwest to maintain a ratio of funded debt to total capitalization not to exceed 0.70 to 1.00 as of the end of any quarter of any fiscal year.

On November 1, 2021, the Company entered into a 364-day term loan credit agreement (the “Credit Agreement”). The Credit Agreement provides for a $1.6 billion delayed-draw term loan (the “Term Loan Facility”) to fund and to pay fees, commissions, and expenses related to the Term Loan Facility and the acquisition by the Company of the equity interests in Questar Pipelines. The Term Loan Facility matures 364 days from the date of the funding of the Term Loan Facility.

The interest rate for the Term Loan Facility is based on either “base rate” or LIBOR, plus an applicable margin in either case. The applicable margin for the Term Loan Facility will be 0% to 0.50% for base rate loans and 0.75% to 1.50% for LIBOR loans, depending on the applicable pricing level in effect. Each of the interest rate spreads will increase by 0.25% at certain time intervals after the funding date. The commitment fee ranges from 0.060% to 0.175% per calendar quarter commencing January 3, 2022, depending on the applicable pricing level in effect. The pricing levels are based on the Company’s senior debt ratings. The interest rate is subject to customary benchmark replacement provisions.

The Credit Agreement contains representations and warranties, affirmative, negative, and financial covenants and events of default substantially similar to the Company’s existing credit facility. Subject to certain exceptions, after the funding date, the Company must make a mandatory prepayment from 100% of the net cash proceeds received by the Company or any of its subsidiaries from any debt offerings or equity issuances and/or 100% of the committed amount under any specified acquisition financings.

LIBOR

Certain rates established at LIBOR are scheduled to be discontinued as a benchmark or reference rate after 2021, while other LIBOR-based rates are scheduled to be discontinued after June 2023. In order to mitigate the impact of a discontinuance on the Company’s and Southwest’s financial condition and results of operations, management will monitor developments and work with lenders to determine the appropriate replacement/alternative reference rate for variable rate debt. At this time the Company and Southwest can provide no assurances as to the impact a LIBOR discontinuance will have on their financial condition or results of operations. Any alternative rate may be less predictable or less attractive than LIBOR.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-URI http://asc.fasb.org/topic&trid=2208564

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Other Comprehensive Income and Accumulated Other Comprehensive Income

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Other Comprehensive Income and Accumulated Other Comprehensive Income

Note 6 – Other Comprehensive Income and Accumulated Other Comprehensive Income

The following information presents 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.

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


	Three Months Ended September 30, 2021						Three Months Ended September 30, 2020
(Thousands of dollars)	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	$	239	$	(56)	$	183	$	289	$	(69)	$	220
Amortization of net actuarial (gain)/loss	11,151		(2,677)		8,474		9,457		(2,270)		7,187
Regulatory adjustment	(9,575)		2,298		(7,277)		(8,394)		2,014		(6,380)
Pension plans other comprehensive income (loss)	1,815		(435)		1,380		1,352		(325)		1,027
FSIRS (designated hedging activities):
Amounts reclassified into net income	544		(131)		413		1,030		(247)		783
FSIRS other comprehensive income (loss)	544		(131)		413		1,030		(247)		783
Total other comprehensive income (loss) - Southwest Gas Corporation	2,359		(566)		1,793		2,382		(572)		1,810
Foreign currency translation adjustments:
Translation adjustments	(2,056)		—		(2,056)		1,024		—		1,024
Foreign currency other comprehensive income (loss)	(2,056)		—		(2,056)		1,024		—		1,024
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	303	$	(566)	$	(263)	$	3,406	$	(572)	$	2,834

	Nine Months Ended September 30, 2021						Nine Months Ended September 30, 2020
(Thousands of dollars)	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	$	719	$	(172)	$	547	$	867	$	(208)	$	659
Amortization of net actuarial (gain)/loss	33,448		(8,028)		25,420		28,372		(6,809)		21,563
Regulatory adjustment	(28,725)		6,894		(21,831)		(25,184)		6,044		(19,140)
Pension plans other comprehensive income (loss)	5,442		(1,306)		4,136		4,055		(973)		3,082
FSIRS (designated hedging activities):
Amounts reclassified into net income	1,632		(392)		1,240		2,703		(649)		2,054
FSIRS other comprehensive income (loss)	1,632		(392)		1,240		2,703		(649)		2,054
Total other comprehensive income (loss) - Southwest Gas Corporation	7,074		(1,698)		5,376		6,758		(1,622)		5,136
Foreign currency translation adjustments:
Translation adjustments	(324)		—		(324)		(1,187)		—		(1,187)
Foreign currency other comprehensive income (loss)	(324)		—		(324)		(1,187)		—		(1,187)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	6,750	$	(1,698)	$	5,052	$	5,571	$	(1,622)	$	3,949


	Twelve Months Ended September 30, 2021						Twelve Months Ended September 30, 2020
(Thousands of dollars)	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)	$	(57,539)	$	13,809	$	(43,730)	$	(71,087)	$	17,061	$	(54,026)
Amortization of prior service cost	1,007		(241)		766		1,185		(284)		901
Amortization of net actuarial (gain)/loss	42,906		(10,298)		32,608		34,216		(8,212)		26,004
Prior service cost	—		—		—		(1,878)		452		(1,426)
Regulatory adjustment	3,894		(935)		2,959		27,803		(6,673)		21,130
Pension plans other comprehensive income (loss)	(9,732)		2,335		(7,397)		(9,761)		2,344		(7,417)
FSIRS (designated hedging activities):
Amounts reclassified into net income	2,176		(523)		1,653		3,539		(850)		2,689
FSIRS other comprehensive income (loss)	2,176		(523)		1,653		3,539		(850)		2,689
Total other comprehensive income (loss) - Southwest Gas Corporation	(7,556)		1,812		(5,744)		(6,222)		1,494		(4,728)
Foreign currency translation adjustments:
Translation adjustments	2,576		—		2,576		(280)		—		(280)
Foreign currency other comprehensive income (loss)	2,576		—		2,576		(280)		—		(280)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	(4,980)	$	1,812	$	(3,168)	$	(6,502)	$	1,494	$	(5,008)

(1)Tax amounts are calculated using a 24% rate. The Company has elected to indefinitely reinvest, in Canada, the earnings of Centuri’s Canadian subsidiaries, thus precluding 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 $828,000 of realized losses (net of tax) related to the remaining balance of Southwest’s previously settled forward-starting interest rate swap (“FSIRS”), included in AOCI at September 30, 2021, will be reclassified into interest expense within the next 6 months (the remainder of the amortization period for the balance) 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 and its Condensed Consolidated Statements of Equity:


	Defined Benefit Plans						FSIRS						Foreign Currency Items
(Thousands of dollars)	Before-Tax		Tax (Expense) Benefit (4)		After-Tax		Before-Tax		Tax (Expense) Benefit (4)		After-Tax		Before-Tax		Tax (Expense) Benefit		After-Tax		AOCI
Beginning Balance AOCI December 31, 2020	$	(77,720)	$	18,653	$	(59,067)	$	(2,719)	$	651	$	(2,068)	$	132	$	—	$	132	$	(61,003)
Translation adjustments	—		—		—		—		—		—		(324)		—		(324)		(324)
Other comprehensive income (loss) before reclassifications	—		—		—		—		—		—		(324)		—		(324)		(324)
FSIRS amount reclassified from AOCI (1)	—		—		—		1,632		(392)		1,240		—		—		—		1,240
Amortization of prior service cost (2)	719		(172)		547		—		—		—		—		—		—		547
Amortization of net actuarial loss (2)	33,448		(8,028)		25,420		—		—		—		—		—		—		25,420
Regulatory adjustment (3)	(28,725)		6,894		(21,831)		—		—		—		—		—		—		(21,831)
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	5,442		(1,306)		4,136		1,632		(392)		1,240		(324)		—		(324)		5,052
Ending Balance AOCI September 30, 2021	$	(72,278)	$	17,347	$	(54,931)	$	(1,087)	$	259	$	(828)	$	(192)	$	—	$	(192)	$	(55,951)

(1)The FSIRS reclassification amount is 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.

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


	Defined Benefit Plans						FSIRS
(Thousands of dollars)	Before-Tax		Tax (Expense) Benefit (8)		After-Tax		Before-Tax		Tax (Expense) Benefit (8)		After-Tax		AOCI
Beginning Balance AOCI December 31, 2020	$	(77,720)	$	18,653	$	(59,067)	$	(2,719)	$	651	$	(2,068)	$	(61,135)
FSIRS amount reclassified from AOCI (5)	—		—		—		1,632		(392)		1,240		1,240
Amortization of prior service cost (6)	719		(172)		547		—		—		—		547
Amortization of net actuarial loss (6)	33,448		(8,028)		25,420		—		—		—		25,420
Regulatory adjustment (7)	(28,725)		6,894		(21,831)		—		—		—		(21,831)
Net current period other comprehensive income attributable to Southwest Gas Corporation	5,442		(1,306)		4,136		1,632		(392)		1,240		5,376
Ending Balance AOCI September 30, 2021	$	(72,278)	$	17,347	$	(54,931)	$	(1,087)	$	259	$	(828)	$	(55,759)

(5) The FSIRS reclassification amount is included in Net interest deductions on Southwest’s Condensed Consolidated Statements of Income.

(6)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).

(7)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).

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

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, 2021		December 31, 2020
Net actuarial loss	$	(469,335)	$	(502,783)
Prior service cost	(1,768)		(2,487)
Less: amount recognized in regulatory assets	398,825		427,550
Recognized in AOCI	$	(72,278)	$	(77,720)

Segment Information

9 Months Ended

Sep. 30, 2021

Segment Reporting [Abstract]

Segment Information

Note 7 – 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.

Centuri accounts for the services provided to Southwest at contractual prices at contract inception. Accounts receivable for these services, which are not eliminated during consolidation, are presented in the table below:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Centuri accounts receivable for services provided to Southwest	$	15,376	$	13,956

Utility infrastructure services total assets increased significantly since December 31, 2020, primarily due to Centuri’s acquisition of Riggs Distler (see Note 8 - Business Acquisitions), as follows:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Centuri segment assets	$	2,671,974	$	1,475,237

In order to reconcile (below) 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 financial information pertaining to the natural gas operations and utility infrastructure services segments is as follows:


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Three Months Ended September 30, 2021
Revenues from external customers	$	255,848	$	606,006	$	—	$	861,854
Intersegment revenues	—		26,842		—		26,842
Total	$	255,848	$	632,848	$	—	$	888,696
Segment net income (loss)	$	(27,544)	$	18,540	$	(2,572)	$	(11,576)

Three Months Ended September 30, 2020
Revenues from external customers	$	210,834	$	548,300	$	—	$	759,134
Intersegment revenues	—		32,092		—		32,092
Total	$	210,834	$	580,392	$	—	$	791,226
Segment net income (loss)	$	(15,973)	$	34,873	$	(627)	$	18,273

(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Nine Months Ended September 30, 2021
Revenues from external customers	$	1,070,576	$	1,450,719	$	—	$	2,521,295
Intersegment revenues	—		74,729		—		74,729
Total	$	1,070,576	$	1,525,448	$	—	$	2,596,024
Segment net income (loss)	$	102,584	$	32,797	$	(4,545)	$	130,836

Nine Months Ended September 30, 2020
Revenues from external customers	$	976,095	$	1,306,481	$	—	$	2,282,576
Intersegment revenues	—		102,217		—		102,217
Total	$	976,095	$	1,408,698	$	—	$	2,384,793
Segment net income (loss)	$	79,568	$	50,936	$	(1,724)	$	128,780


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Twelve Months Ended September 30, 2021
Revenues from external customers	$	1,445,066	$	1,957,667	$	—	$	3,402,733
Intersegment revenues	—		107,371		—		107,371
Total	$	1,445,066	$	2,065,038	$	—	$	3,510,104
Segment net income (loss)	$	182,134	$	56,723	$	(4,477)	$	234,380

Twelve Months Ended September 30, 2020
Revenues from external customers	$	1,355,666	$	1,738,430	$	—	$	3,094,096
Intersegment revenues	—		138,834		—		138,834
Total	$	1,355,666	$	1,877,264	$	—	$	3,232,930
Segment net income (loss)	$	155,993	$	66,615	$	(2,110)	$	220,498

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Business Acquisitions

9 Months Ended

Sep. 30, 2021

Business Combination and Asset Acquisition [Abstract]

Business Acquisitions

Note 8 - Business Acquisitions

On August 27, 2021, the Company, through its subsidiaries, led principally by Centuri, completed the acquisition of a privately held regional infrastructure services business, Drum Parent, Inc. (“Drum”), for $830.4 million in cash consideration, and also assumed a long-term financing lease obligation. Drum, and its primary subsidiary Riggs Distler & Company, Inc. (“Riggs Distler”), are now wholly owned subsidiaries of the Company.

The acquisition extended the utility services operations in the northeastern region of the U.S. and provides additional opportunities for expansion of the amount of work Centuri performs for electric and gas utilities. Funding for the acquisition was provided by proceeds from Centuri’s new term loan facility, as described in Note 5 – Debt.

The Company is currently performing a detailed valuation analysis of the assets and liabilities of the acquired company, which was substantially completed during the third quarter of 2021. Certain payments were estimated as of the acquisition date and will be adjusted when paid. The necessary analysis will consider acquired intangibles (including customer relationships, trademarks, and backlog). Based on preliminary results, a substantial portion of the purchase price will be allocated to goodwill and other finite-lived intangible assets.

Assets acquired and liabilities assumed in the transaction were recorded at their acquisition date fair values. Transaction costs associated with the acquisition were expensed as incurred. 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 businesses, 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 those indicated above. The gross contractual receivable is $81 million, exclusive of $12 million representing specific customer accounts that were deemed uncollectible. Of the $12 million, any amounts subsequently collected prior to December 31, 2021 would pass to the sellers. Due to the estimations made, the final purchase accounting has not yet been completed. Further refinement is expected to occur, including potential changes to income taxes, fixed assets, and intangibles.

The preliminary estimated fair values of assets acquired and liabilities assumed as of August 27, 2021, are as follows (in millions of dollars):


Cash and cash equivalents	$	1.9
Accounts receivable	69.1
Contract assets	40.1
Income taxes receivable, net	0.7
Right of use assets under operating leases	1.5
Prepaid expenses	5.2
Property and equipment	118.1
Intangible assets	335.0
Goodwill	446.8
Total assets acquired	1,018.4

Trade and other payables	46.2
Finance lease obligations	27.5
Contract liabilities	12.7
Operating lease obligations	1.5
Other liabilities	5.3
Deferred tax liabilities	94.8
Total liabilities assumed	188.0
Net assets acquired	$	830.4

The amounts allocated to major classes of intangibles are as follows:


(Thousands of dollars)	Estimated fair Value		Estimated Weighted Average Useful Life in Years
Backlog	$	5,000	1
Trade names	60,000		15
Customer relationships	270,000		19
	$	335,000

The Company incurred and expensed acquisition costs of $14 million which were included in Utility infrastructure services expenses on the Company’s Condensed Consolidated Statement of Income. Acquisition-related costs of $13.2 million and $14 million were incurred during the three and nine months ended September 30, 2021, respectively.

The preliminary allocation of the purchase price of Drum 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 Drum was deemed a stock purchase for tax purposes, only pre-acquisition goodwill of $76 million that was historically tax-deductible by Riggs will continue to be deductible for tax purposes by the Company.

The following unaudited pro forma financial information reflects the consolidated results of operations of the Company assuming the acquisition had taken place on January 1, 2020. The most significant pro forma adjustments relate to: (i) reflecting approximately $30 million in transaction costs (incurred by Centuri and Riggs Distler) in the nine months ended September 30, 2020, and excluding such costs from the three and nine month periods ended September 30, 2021, and (ii) reflecting incremental interest expense related to the new loan facility of $7 million and $27 million in the three and nine month periods, respectively, ended September 30, 2021, and approximately $9 million and $24.5 million in the comparable periods in 2020. This information is preliminary in nature and subject to change based upon final purchase price adjustments. Amounts are in thousands of dollars, except per share amounts.


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Total operating revenues	$	956,120	$	907,512	$	2,903,658	$	2,702,062
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$	(8,918)	$	12,688	$	120,828	$	84,049
Basic earnings (loss) per share	$	(0.15)	$	0.23	$	2.06	$	1.51
Diluted earnings (loss) per share	$	(0.15)	$	0.23	$	2.06	$	1.51

Actual results from operations for Riggs Distler, excluding transaction costs and interest expense on acquisition related debt incurred by Centuri, included in the Consolidated Statements of Income since the date of acquisition are as follows (in thousands of dollars):


	Nine Months Ended September 30, 2021
Utility infrastructure services revenues	$	49,520
Net income attributable to Southwest Gas Holdings, Inc.	$	1,646

Background, Organization, and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
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). In October 2021, Southwest Gas Holdings, Inc. (the “Company”) entered into an agreement with Dominion Energy Questar Corporation, a wholly owned subsidiary of Dominion Energy, Inc., to acquire all equity interests in Dominion Energy Questar Pipeline, LLC and related entities (“Questar Pipelines”). Upon closing, Questar Pipelines will operate as part of a standalone subsidiary of the Company, and will undergo new branding at or subsequent to close. The agreement provides for consideration of $1.545 billion in cash (subject to certain adjustments) and assumption of approximately $430 million of existing long-term debt. The agreement contains certain termination rights, including a mutual termination right exercisable at any time and a unilateral termination right exercisable by either party if certain conditions have not been met by December 31, 2021 (the initial termination date), subject to an extension unilaterally exercisable by either party if certain conditions have not been met, subsequently extending the initial termination date through June 30, 2022. The completion of this transaction is subject to closing conditions, including the expiration or termination of any waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, and approval of certain aspects of the transaction by the Federal Communications Commission. The operations to be acquired would further diversify the Company’s business with an expansion of regulated interstate natural gas pipelines and underground storage services as part of the jurisdiction of the Federal Energy Regulatory Commission (the “FERC”), thereby expanding transportation services into Utah, Wyoming, and Colorado. The Company plans to initially fund this acquisition with a new 364-day term loan, followed by permanent financing. See Note 5 – Debt for more information. 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 primarily from installation, replacement, repair, and maintenance of energy distribution systems. 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”), Linetec Services, LLC (“Linetec”), and Riggs Distler & Company, Inc. (“Riggs Distler”). 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.
Basis of Presentation	Basis of Presentation. The condensed consolidated financial statements of Southwest Gas Holdings, Inc. and subsidiaries 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. 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 as of 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. In association with the novel Coronavirus (“COVID-19”) pandemic environment, utility operations, and to a large extent, utility infrastructure services, were deemed “essential services.” Management has considered the impact of the pandemic and adjusted certain estimates, where relevant, in the preparation of the condensed consolidated financial statements. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the 2020 Annual Report to Stockholders, which is incorporated by reference into the 2020 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, 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 of the Company include $55 million of money market fund investments at September 30, 2021, and an insignificant amount at December 31, 2020. The money market fund investments for Southwest were insignificant at both balance sheet dates. These investments 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 include customer advances applied as contributions toward utility construction activity, and capital expenditures that were not yet paid as of period-end reporting dates, but rather were included in accounts payable. Typical activities that represent aspects of both non-cash investing and non-cash financing activities relate to right-of-use assets obtained in exchange for lease liabilities (including, at times, lease terminations and modifications). Amounts related to these collective activities were immaterial for the periods presented herein. See also Prepaid and other current assets below.
Intercompany Transactions	Intercompany Transactions. Centuri recognizes revenues generated from contracts with Southwest (see Note 7 – Segment Information). 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.
Accounts Receivable, net of allowances	Accounts Receivable, net of allowances. Business activity with respect to natural gas utility operations is conducted with customers located within the three-state region of Arizona, Nevada, and California. Southwest’s accounts receivable are short-term in nature with no billing due dates customarily extending beyond one month, with customers’ credit worthiness assessed upon account creation by evaluation of other utility service and related payment history. Southwest lifted the moratorium on disconnection of natural gas service for non-payment in Arizona and Nevada in September 2021, which was initiated (at the same time as a moratorium on late fees) in March 2020 in response to the COVID-19 pandemic. The moratorium on disconnection continues to be in place for California, and is expected to be lifted in the fourth quarter of 2021. Southwest recommenced assessing late fees on past-due balances in Arizona and Nevada in April 2021, and expects to recommence late fees in California in the fourth quarter of 2021. Southwest is actively working with customers experiencing financial hardship by means of flexible payment options. Management continues to monitor expected credit losses in light of the impact of COVID-19. The allowance for uncollectible accounts receivable balances as of September 30, 2021 reflects the expected impact from the pandemic on balances as of that date, including consideration of customers’ ability to pay those amounts that are due. Utility infrastructure services contracts receivable are recorded at face amounts less an allowance for doubtful accounts. Centuri’s customers are generally investment-grade gas and electric utility companies for which Centuri has historically recognized an insignificant amount of write-offs. Centuri has not been significantly impacted, nor does it anticipate it will experience significant difficulty in collecting amounts due, as a result of the current environment surrounding COVID-19 given the nature of its customers. Activity between periods in the allowance for uncollectible accounts and the balances as of the periods presented within the Company’s and Southwest’s financial statements were not material to the condensed consolidated financial statements overall.
Deferred Purchased Gas Costs	Deferred Purchased Gas Costs. The various regulatory commissions have established procedures to enable Southwest to adjust its billing rates for changes in the cost of natural gas purchased. The difference between the current cost of gas purchased and the cost of gas recovered in billed rates is deferred. Generally, these deferred amounts are recovered or refunded within one year. In mid-February 2021, the central U.S. (from south Texas to North Dakota and the eastern Rocky Mountains) experienced extreme cold temperatures, which increased natural gas demand and caused supply issues due to wellhead freeze-offs, power outages, or other adverse operating conditions upstream of Southwest’s distribution systems. These conditions caused daily natural gas prices to reach unprecedented levels. During this time, Southwest secured natural gas supplies, albeit at substantially higher prices, maintaining service to its customers. The incremental cost for these supplies was approximately $250 million, funded using a 364-day $250 million term loan executed in March 2021 (see Note 5 – Debt). The incremental gas costs are expected to continue to be collected from customers through the purchased gas adjustment (“PGA”) mechanisms. Following the extreme weather event, an interstate transmission pipeline company billed Southwest, in addition to customary transmission costs, $65 million (later reduced to approximately $55 million) for pipeline imbalance charges, allegedly incurred during the period of the pipeline’s critical operation condition. However, Southwest formally disputed the imbalance charges, in addition to interest on that amount, believing that no amounts were due to the pipeline. In June 2021, the interstate transmission pipeline company requested approval from the Federal Energy Regulatory Commission (the “FERC”) to waive these imbalance charges and interest, affirming that they had the authority to elect the option to waive the underlying charges based on their tariff, but were seeking approval by the FERC for purposes of transparency and regulatory certainty. In August 2021, FERC approval was received. Consequently, no amounts were recognized by Southwest related to the original charge from the pipeline.
Prepaid and other current assets	Prepaid and other current assets. Prepaid and other current assets includes gas pipe materials and operating supplies of $55 million at September 30, 2021 and $50 million at December 31, 2020 (carried at weighted average cost). In the third quarter of 2021, the Company and Southwest classified certain assets associated with its previous corporate headquarters as held for sale. As a result, the Company and Southwest reclassified approximately $31 million from Net utility plant to Prepaid and other current assets on their respective Condensed Consolidated Balance Sheets during the third quarter of 2021; this was a non-cash item and therefore did not impact the Company’s or Southwest’s respective Condensed Consolidated Statements of Cash Flows.
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 they remained consistent between periods presented below, and that no change was necessary with regard to the level at which goodwill is assessed for impairment.
Other current liabilities	Other Current Liabilities. Management recognizes in its balance sheets various liabilities that are expected to be settled through future cash payment within the next twelve months, including amounts payable under regulatory mechanisms, customary accrued expenses for employee compensation and benefits, declared but unpaid dividends, and miscellaneous other accrued liabilities. Other current liabilities for the Company includes $35.9 million and $32.6 million of dividends declared as of September 30, 2021 and December 31, 2020, respectively, as well as liabilities included as part of the Riggs Distler acquisition.
Earnings Per Share	Earnings Per Share. Basic earnings per share (“EPS”) in each period of this report were calculated by dividing net income attributable to Southwest Gas Holdings, Inc. by the weighted-average number of shares during those periods. Diluted EPS includes additional weighted-average common stock equivalents (performance shares and restricted stock units). Unless otherwise noted, the term “Earnings Per Share” refers to Basic EPS.
Recent Accounting Standards Updates	Recent Accounting Standards Updates. Accounting pronouncements adopted in 2021: In December 2019, the Financial Accounting Standards Board (the “FASB”) issued ASU 2019-12 “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes.” The update simplifies the accounting for income taxes by removing certain exceptions to the general principles, as well as improving consistent application in Topic 740 by clarifying and amending existing guidance. The Company and Southwest adopted the update in the first quarter of 2021, the impact of which was not material to the condensed consolidated financial statements of the Company or Southwest. Recently issued accounting pronouncements that will be effective after 2021: In March 2020, the FASB issued ASU 2020-04 “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” The update provides optional guidance for a limited time to ease the potential burden in accounting for, or recognizing the effects of, reference rate reform on financial reporting, including when modifying a contract (during the eligibility period covered by the update to Topic 848) to replace a reference rate affected by such reform. The update applies only to contracts and hedging relationships that reference the London Interbank Offered Rate (“LIBOR”) or another rate expected to be discontinued due to reference rate reform. The guidance was eligible to be applied upon issuance on March 12, 2020, and can generally be applied through December 31, 2022, but to date, no further updates have occurred that would extend the optional guidance to the full tenor of LIBOR expiration dates occurring after 2022. Management will monitor the impacts this update might have on the Company’s and Southwest’s consolidated financial statements and disclosures, and will reflect such appropriately, in the event that the optional guidance is elected. It will also monitor further FASB action, if any, in regard to the full tenor of LIBOR expiration dates. See also LIBOR discussion in Note 5 – Debt. In August 2020, the FASB issued ASU 2020-06 “Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity.” The update, amongst other amendments, improves the guidance related to the disclosures and earnings-per-share for convertible instruments and contracts in an entity’s own equity. The update is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years; early adoption is permitted. Management is evaluating what impacts, if any, this update might have on the Company’s consolidated financial statements and disclosures.

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

9 Months Ended

Sep. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Other Property and Investments

Other property and investments on the Condensed Consolidated Balance Sheets includes:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Southwest Gas Corporation:
Net cash surrender value of COLI policies	$	147,187	$	140,874
Other property	2,739		2,737
Total Southwest Gas Corporation	149,926		143,611
Centuri property, equipment, and intangibles	1,592,461		1,089,414
Centuri accumulated provision for depreciation and amortization	(468,206)		(422,741)
Other property and investments	31,153		23,961
Total Southwest Gas Holdings, Inc.	$	1,305,334	$	834,245

Schedule of Goodwill

Goodwill on Southwest’s and the Company’s Condensed Consolidated Balance Sheets includes:


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Total Company
December 31, 2020	$	10,095	$	335,089	$	345,184
Additional goodwill from Riggs Distler acquisition	—		446,794		446,794
Foreign currency translation adjustment	—		(76)		(76)
September 30, 2021	$	10,095	$	781,807	$	791,902

Schedule of Significant Items Included in Other Income (Deductions)

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


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	—	$	4,500	$	5,800	$	1,000	$	14,000	$	7,200
Interest income	1,365		1,412		3,312		3,214		4,113		4,630
Equity AFUDC	—		1,232		—		3,413		1,311		4,395
Other components of net periodic benefit cost	(3,506)		(5,005)		(10,516)		(15,016)		(15,522)		(18,780)
Miscellaneous income and (expense)	(2,146)		(388)		(3,498)		(3,558)		(4,447)		(5,060)
Southwest Gas Corporation - total other income (deductions)	(4,287)		1,751		(4,902)		(10,947)		(545)		(7,615)
Utility infrastructure services segment:

Foreign transaction gain (loss)	(7)		—		(19)		(16)		(19)		(16)
Miscellaneous income and (expense)	1,182		48		946		(91)		846		(194)
Centuri - total other income (deductions)	1,175		48		927		(107)		827		(210)
Corporate and administrative	—		—		—		8		—		37
Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	(3,112)	$	1,799	$	(3,975)	$	(11,046)	$	282	$	(7,788)

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, 2020	$	165,716
Net income attributable to redeemable noncontrolling interest	5,189
Redemption value adjustment	12,642
Balance, September 30, 2021	$	183,547

Schedule of Earnings Per Share, Basic and Diluted

A reconciliation of the denominator used in Basic and Diluted EPS calculations is shown in the following table:


	Three Months Ended September 30,		Nine Months Ended September 30,		Twelve Months Ended September 30,
(In thousands)	2021	2020	2021	2020	2021	2020
Weighted average basic shares	59,688	56,271	58,639	55,683	58,209	55,508
Effect of dilutive securities:
Management Incentive Plan shares	—	—	—	—	—	3
Restricted stock units (1)	128	86	103	70	103	66
Weighted average diluted shares	59,816	56,357	58,742	55,753	58,312	55,577

Components of Net Periodic Benefit Cost (Tables)

9 Months Ended

Sep. 30, 2021

Retirement Benefits [Abstract]

Schedule of Net Periodic Benefit Costs


	Qualified Retirement Plan
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	10,289	$	8,576	$	30,869	$	25,725	$	39,443	$	32,191
Interest cost	10,108		11,388		30,324		34,165		41,714		46,416
Expected return on plan assets	(18,088)		(16,324)		(54,264)		(48,972)		(70,588)		(64,033)
Amortization of net actuarial loss	10,489		9,006		31,467		27,019		40,473		32,608
Net periodic benefit cost	$	12,798	$	12,646	$	38,396	$	37,937	$	51,042	$	47,182

	SERP
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	131	$	97	$	394	$	292	$	491	$	359
Interest cost	358		401		1,074		1,204		1,474		1,644
Amortization of net actuarial loss	661		451		1,981		1,353		2,433		1,608
Net periodic benefit cost	$	1,150	$	949	$	3,449	$	2,849	$	4,398	$	3,611

	PBOP
	September 30,
	Three Months				Nine Months				Twelve Months
	2021		2020		2021		2020		2021		2020
(Thousands of dollars)
Service cost	$	423	$	395	$	1,269	$	1,186	$	1,664	$	1,505
Interest cost	549		646		1,645		1,936		2,291		2,697
Expected return on plan assets	(810)		(852)		(2,430)		(2,556)		(3,282)		(3,345)
Amortization of prior service costs	239		289		719		867		1,007		1,185

Net periodic benefit cost	$	401	$	478	$	1,203	$	1,433	$	1,680	$	2,042

Revenue (Tables)

9 Months Ended

Sep. 30, 2021

Revenue from Contract with Customer [Abstract]

Summary of Revenue Disaggregated by Service Type and Contract Type


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Residential	$	147,326	$	131,008	$	743,791	$	690,861	$	1,011,450	$	957,379
Small commercial	48,283		35,204		185,774		159,122		248,193		228,720
Large commercial	14,199		9,942		40,030		32,588		52,075		45,493
Industrial/other	9,608		5,888		30,352		19,089		37,505		25,435
Transportation	21,884		21,040		68,217		65,281		91,151		89,364
Revenue from contracts with customers	241,300		203,082		1,068,164		966,941		1,440,374		1,346,391
Alternative revenue program revenues (deferrals)	12,569		9,199		(5,335)		9,545		(2,740)		7,629
Other revenues (1)	1,979		(1,447)		7,747		(391)		7,432		1,646
Total Gas operating revenues	$	255,848	$	210,834	$	1,070,576	$	976,095	$	1,445,066	$	1,355,666


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Service Types:
Gas infrastructure services	$	393,122	$	387,578	$	961,836	$	935,444	$	1,287,552	$	1,288,468
Electric power infrastructure services	155,456		115,386		347,061		282,992		475,895		346,432
Other	84,270		77,428		216,551		190,262		301,591		242,364
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264


	Three Months Ended September 30,				Nine Months Ended September 30,				Twelve Months Ended September 30,
(Thousands of dollars)	2021		2020		2021		2020		2021		2020
Contract Types:
Master services agreement	$	467,869	$	437,914	$	1,160,199	$	1,076,961	$	1,573,247	$	1,438,540
Bid contract	164,979		142,478		365,249		331,737		491,791		438,724
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264

Unit price contracts	$	406,404	$	377,284	$	1,002,779	$	985,673	$	1,373,746	$	1,359,352
Fixed price contracts	64,632		46,379		149,681		109,935		197,447		142,356
Time and materials contracts	161,812		156,729		372,988		313,090		493,845		375,556
Total Utility infrastructure services revenues	$	632,848	$	580,392	$	1,525,448	$	1,408,698	$	2,065,038	$	1,877,264

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, 2021		December 31, 2020
Contracts receivable, net	$	381,387	$	278,316
Revenue earned on contracts in progress in excess of billings	207,318		96,996
Amounts billed in excess of revenue earned on contracts	19,954		4,507

Schedule of Utility Infrastructure Services Contracts Receivable

Utility infrastructure services contracts receivable consists of the following:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Billed on completed contracts and contracts in progress	$	380,484	$	273,778
Other receivables	2,844		6,692
Contracts receivable, gross	383,328		280,470
Allowance for doubtful accounts	(1,941)		(2,154)
Contracts receivable, net	$	381,387	$	278,316

Common Stock (Tables)

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Schedule of Common Stock Activity

The following table provides the activity under the Equity Shelf Program for the three-month and life-to-date periods ended September 30, 2021:


	Three Months Ended		Life-To-Date Ended
	September 30, 2021
Gross proceeds	$	87,819,931	$	158,180,343
Less: agent commissions	(878,199)		(1,581,803)
Net proceeds	$	86,941,732	$	156,598,540
Number of shares sold	1,251,810		2,302,407
Weighted average price per share	$	70.15	$	68.70

Debt (Tables)

9 Months Ended

Sep. 30, 2021

Debt Disclosure [Abstract]

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


	September 30, 2021				December 31, 2020
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 6.1%, due 2041	$	125,000	$	167,755	$	125,000	$	174,858
Notes, 3.875%, due 2022	250,000		252,208		250,000		258,825
Notes, 4.875%, due 2043	250,000		307,385		250,000		317,190
Notes, 3.8%, due 2046	300,000		326,058		300,000		347,046
Notes, 3.7%, due 2028	300,000		331,536		300,000		344,553
Notes, 4.15%, due 2049	300,000		343,950		300,000		370,278
Notes, 2.2%, due 2030	450,000		447,287		450,000		474,552
Notes, 3.18%, due 2051	300,000		291,351		—		—
8% Series, due 2026	75,000		94,752		75,000		99,723
Medium-term notes, 7.78% series, due 2022	25,000		25,513		25,000		26,663
Medium-term notes, 7.92% series, due 2027	25,000		31,936		25,000		33,802
Medium-term notes, 6.76% series, due 2027	7,500		9,116		7,500		9,613
Unamortized discount and debt issuance costs	(20,727)				(17,822)
	2,386,773				2,089,678
Revolving credit facility and commercial paper	—		—		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	(1,916)				(1,472)
	198,084				198,528
Less: current maturities	(275,000)				—
Long-term debt, less current maturities - Southwest Gas Corporation	$	2,309,857			$	2,438,206
Centuri:
Centuri term loan facility	$	1,145,000	$	1,146,431	$	226,648	$	230,824
Unamortized debt issuance costs	(25,385)				(820)
	1,119,615				225,828
Centuri secured revolving credit facility	112,236		112,348		26,626		26,645
Centuri other debt obligations	54,346		52,682		81,973		84,246
Less: current maturities	(22,271)				(40,433)
Long-term debt, less current maturities - Centuri	$	1,263,926			$	293,994
Consolidated Southwest Gas Holdings, Inc.:
Southwest Gas Corporation long-term debt	$	2,584,857			$	2,438,206
Centuri long-term debt	1,286,197				334,427
Less: current maturities	(297,271)				(40,433)
Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	3,573,783			$	2,732,200

- 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

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+ Details

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

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


	Three Months Ended September 30, 2021						Three Months Ended September 30, 2020
(Thousands of dollars)	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	$	239	$	(56)	$	183	$	289	$	(69)	$	220
Amortization of net actuarial (gain)/loss	11,151		(2,677)		8,474		9,457		(2,270)		7,187
Regulatory adjustment	(9,575)		2,298		(7,277)		(8,394)		2,014		(6,380)
Pension plans other comprehensive income (loss)	1,815		(435)		1,380		1,352		(325)		1,027
FSIRS (designated hedging activities):
Amounts reclassified into net income	544		(131)		413		1,030		(247)		783
FSIRS other comprehensive income (loss)	544		(131)		413		1,030		(247)		783
Total other comprehensive income (loss) - Southwest Gas Corporation	2,359		(566)		1,793		2,382		(572)		1,810
Foreign currency translation adjustments:
Translation adjustments	(2,056)		—		(2,056)		1,024		—		1,024
Foreign currency other comprehensive income (loss)	(2,056)		—		(2,056)		1,024		—		1,024
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	303	$	(566)	$	(263)	$	3,406	$	(572)	$	2,834

	Nine Months Ended September 30, 2021						Nine Months Ended September 30, 2020
(Thousands of dollars)	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	$	719	$	(172)	$	547	$	867	$	(208)	$	659
Amortization of net actuarial (gain)/loss	33,448		(8,028)		25,420		28,372		(6,809)		21,563
Regulatory adjustment	(28,725)		6,894		(21,831)		(25,184)		6,044		(19,140)
Pension plans other comprehensive income (loss)	5,442		(1,306)		4,136		4,055		(973)		3,082
FSIRS (designated hedging activities):
Amounts reclassified into net income	1,632		(392)		1,240		2,703		(649)		2,054
FSIRS other comprehensive income (loss)	1,632		(392)		1,240		2,703		(649)		2,054
Total other comprehensive income (loss) - Southwest Gas Corporation	7,074		(1,698)		5,376		6,758		(1,622)		5,136
Foreign currency translation adjustments:
Translation adjustments	(324)		—		(324)		(1,187)		—		(1,187)
Foreign currency other comprehensive income (loss)	(324)		—		(324)		(1,187)		—		(1,187)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	6,750	$	(1,698)	$	5,052	$	5,571	$	(1,622)	$	3,949


	Twelve Months Ended September 30, 2021						Twelve Months Ended September 30, 2020
(Thousands of dollars)	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)	$	(57,539)	$	13,809	$	(43,730)	$	(71,087)	$	17,061	$	(54,026)
Amortization of prior service cost	1,007		(241)		766		1,185		(284)		901
Amortization of net actuarial (gain)/loss	42,906		(10,298)		32,608		34,216		(8,212)		26,004
Prior service cost	—		—		—		(1,878)		452		(1,426)
Regulatory adjustment	3,894		(935)		2,959		27,803		(6,673)		21,130
Pension plans other comprehensive income (loss)	(9,732)		2,335		(7,397)		(9,761)		2,344		(7,417)
FSIRS (designated hedging activities):
Amounts reclassified into net income	2,176		(523)		1,653		3,539		(850)		2,689
FSIRS other comprehensive income (loss)	2,176		(523)		1,653		3,539		(850)		2,689
Total other comprehensive income (loss) - Southwest Gas Corporation	(7,556)		1,812		(5,744)		(6,222)		1,494		(4,728)
Foreign currency translation adjustments:
Translation adjustments	2,576		—		2,576		(280)		—		(280)
Foreign currency other comprehensive income (loss)	2,576		—		2,576		(280)		—		(280)
Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	(4,980)	$	1,812	$	(3,168)	$	(6,502)	$	1,494	$	(5,008)

Schedule of Rollforward of Accumulated Other Comprehensive Income

The following table represents a rollforward of AOCI, presented on the Company’s Condensed Consolidated Balance Sheets and its Condensed Consolidated Statements of Equity:


	Defined Benefit Plans						FSIRS						Foreign Currency Items
(Thousands of dollars)	Before-Tax		Tax (Expense) Benefit (4)		After-Tax		Before-Tax		Tax (Expense) Benefit (4)		After-Tax		Before-Tax		Tax (Expense) Benefit		After-Tax		AOCI
Beginning Balance AOCI December 31, 2020	$	(77,720)	$	18,653	$	(59,067)	$	(2,719)	$	651	$	(2,068)	$	132	$	—	$	132	$	(61,003)
Translation adjustments	—		—		—		—		—		—		(324)		—		(324)		(324)
Other comprehensive income (loss) before reclassifications	—		—		—		—		—		—		(324)		—		(324)		(324)
FSIRS amount reclassified from AOCI (1)	—		—		—		1,632		(392)		1,240		—		—		—		1,240
Amortization of prior service cost (2)	719		(172)		547		—		—		—		—		—		—		547
Amortization of net actuarial loss (2)	33,448		(8,028)		25,420		—		—		—		—		—		—		25,420
Regulatory adjustment (3)	(28,725)		6,894		(21,831)		—		—		—		—		—		—		(21,831)
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.	5,442		(1,306)		4,136		1,632		(392)		1,240		(324)		—		(324)		5,052
Ending Balance AOCI September 30, 2021	$	(72,278)	$	17,347	$	(54,931)	$	(1,087)	$	259	$	(828)	$	(192)	$	—	$	(192)	$	(55,951)

(1)The FSIRS reclassification amount is 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).

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

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


	Defined Benefit Plans						FSIRS
(Thousands of dollars)	Before-Tax		Tax (Expense) Benefit (8)		After-Tax		Before-Tax		Tax (Expense) Benefit (8)		After-Tax		AOCI
Beginning Balance AOCI December 31, 2020	$	(77,720)	$	18,653	$	(59,067)	$	(2,719)	$	651	$	(2,068)	$	(61,135)
FSIRS amount reclassified from AOCI (5)	—		—		—		1,632		(392)		1,240		1,240
Amortization of prior service cost (6)	719		(172)		547		—		—		—		547
Amortization of net actuarial loss (6)	33,448		(8,028)		25,420		—		—		—		25,420
Regulatory adjustment (7)	(28,725)		6,894		(21,831)		—		—		—		(21,831)
Net current period other comprehensive income attributable to Southwest Gas Corporation	5,442		(1,306)		4,136		1,632		(392)		1,240		5,376
Ending Balance AOCI September 30, 2021	$	(72,278)	$	17,347	$	(54,931)	$	(1,087)	$	259	$	(828)	$	(55,759)

(5) The FSIRS reclassification amount is included in Net interest deductions on Southwest’s Condensed Consolidated Statements of Income.

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

Schedule of 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, 2021		December 31, 2020
Net actuarial loss	$	(469,335)	$	(502,783)
Prior service cost	(1,768)		(2,487)
Less: amount recognized in regulatory assets	398,825		427,550
Recognized in AOCI	$	(72,278)	$	(77,720)

Segment Information (Tables)

9 Months Ended

Sep. 30, 2021

Segment Reporting [Abstract]

Schedule of Accounts Receivable for Services

Accounts receivable for these services, which are not eliminated during consolidation, are presented in the table below:


(Thousands of dollars)	September 30, 2021		December 31, 2020
Centuri accounts receivable for services provided to Southwest	$	15,376	$	13,956

Schedule of Utility Infrastructure Services Assets


(Thousands of dollars)	September 30, 2021		December 31, 2020
Centuri segment assets	$	2,671,974	$	1,475,237

Schedule of Segment Reporting Information

The financial information pertaining to the natural gas operations and utility infrastructure services segments is as follows:


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Three Months Ended September 30, 2021
Revenues from external customers	$	255,848	$	606,006	$	—	$	861,854
Intersegment revenues	—		26,842		—		26,842
Total	$	255,848	$	632,848	$	—	$	888,696
Segment net income (loss)	$	(27,544)	$	18,540	$	(2,572)	$	(11,576)

Three Months Ended September 30, 2020
Revenues from external customers	$	210,834	$	548,300	$	—	$	759,134
Intersegment revenues	—		32,092		—		32,092
Total	$	210,834	$	580,392	$	—	$	791,226
Segment net income (loss)	$	(15,973)	$	34,873	$	(627)	$	18,273

(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Nine Months Ended September 30, 2021
Revenues from external customers	$	1,070,576	$	1,450,719	$	—	$	2,521,295
Intersegment revenues	—		74,729		—		74,729
Total	$	1,070,576	$	1,525,448	$	—	$	2,596,024
Segment net income (loss)	$	102,584	$	32,797	$	(4,545)	$	130,836

Nine Months Ended September 30, 2020
Revenues from external customers	$	976,095	$	1,306,481	$	—	$	2,282,576
Intersegment revenues	—		102,217		—		102,217
Total	$	976,095	$	1,408,698	$	—	$	2,384,793
Segment net income (loss)	$	79,568	$	50,936	$	(1,724)	$	128,780


(Thousands of dollars)	Natural Gas Operations		Utility Infrastructure Services		Other		Total
Twelve Months Ended September 30, 2021
Revenues from external customers	$	1,445,066	$	1,957,667	$	—	$	3,402,733
Intersegment revenues	—		107,371		—		107,371
Total	$	1,445,066	$	2,065,038	$	—	$	3,510,104
Segment net income (loss)	$	182,134	$	56,723	$	(4,477)	$	234,380

Twelve Months Ended September 30, 2020
Revenues from external customers	$	1,355,666	$	1,738,430	$	—	$	3,094,096
Intersegment revenues	—		138,834		—		138,834
Total	$	1,355,666	$	1,877,264	$	—	$	3,232,930
Segment net income (loss)	$	155,993	$	66,615	$	(2,110)	$	220,498

Business Acquisitions (Tables)

9 Months Ended

Sep. 30, 2021

Business Combination and Asset Acquisition [Abstract]

Summary of Fair Values of Assets Acquired and Liabilities Assumed

The preliminary estimated fair values of assets acquired and liabilities assumed as of August 27, 2021, are as follows (in millions of dollars):


Cash and cash equivalents	$	1.9
Accounts receivable	69.1
Contract assets	40.1
Income taxes receivable, net	0.7
Right of use assets under operating leases	1.5
Prepaid expenses	5.2
Property and equipment	118.1
Intangible assets	335.0
Goodwill	446.8
Total assets acquired	1,018.4

Trade and other payables	46.2
Finance lease obligations	27.5
Contract liabilities	12.7
Operating lease obligations	1.5
Other liabilities	5.3
Deferred tax liabilities	94.8
Total liabilities assumed	188.0
Net assets acquired	$	830.4

Schedule of Finite-Lived Intangible Assets Acquired

The amounts allocated to major classes of intangibles are as follows:


(Thousands of dollars)	Estimated fair Value		Estimated Weighted Average Useful Life in Years
Backlog	$	5,000	1
Trade names	60,000		15
Customer relationships	270,000		19
	$	335,000

Business Acquisition, Pro Forma Information


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Total operating revenues	$	956,120	$	907,512	$	2,903,658	$	2,702,062
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$	(8,918)	$	12,688	$	120,828	$	84,049
Basic earnings (loss) per share	$	(0.15)	$	0.23	$	2.06	$	1.51
Diluted earnings (loss) per share	$	(0.15)	$	0.23	$	2.06	$	1.51


	Nine Months Ended September 30, 2021
Utility infrastructure services revenues	$	49,520
Net income attributable to Southwest Gas Holdings, Inc.	$	1,646

Background, Organization, and Summary of Significant Accounting Policies - Narratives (Details)	1 Months Ended			2 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Feb. 28, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($) state	May 31, 2021 USD ($)	Sep. 30, 2021 USD ($) state	Dec. 31, 2020 USD ($)	Nov. 30, 2018
Significant Accounting Policies [Line Items]
Number of states in which entity operates \| state					3		3
Accounts receivable, extending period							1 month
Deferred purchased gas costs, recovered or refunded period							1 year
Deferred purchased gas costs, estimated incremental costs				$ 250,000,000
Deferred purchased gas costs, pipeline imbalance charges			$ 65,000,000			$ 55,000,000
Goodwill impairment							$ 0
Dividends declared but not yet paid					$ 35,900,000		35,900,000	$ 32,600,000
Self-insured retention amount					1,000,000		1,000,000
Threshold amount above self-insured retention					4,000,000		4,000,000
Loss contingency, maximum					5,000,000		5,000,000
Loss contingency accrual					5,000,000		5,000,000
Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments					55,000,000		55,000,000	0
Subsequent Event \| Questar Pipelines
Significant Accounting Policies [Line Items]
Payments to acquire business	$ 1,545,000,000
Assumption of long-term debt in business acquisition	$ 430,000,000
Linetec
Significant Accounting Policies [Line Items]
Ownership percentage by noncontrolling owners									20.00%
Gas Pipe Materials and Supplies \| Prepaid and other current assets
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies					55,000,000		$ 55,000,000	50,000,000
Southwest Gas Corporation
Significant Accounting Policies [Line Items]
Reclassification amount from Net utility plant to Prepaid and other current assets					$ 31,000,000
Southwest Gas Corporation \| Money Market Funds
Significant Accounting Policies [Line Items]
Money market fund investments								$ 0
Southwest Gas Corporation \| $250 Million Term Loan
Significant Accounting Policies [Line Items]
Debt instrument, term		364 days
Debt instrument, face amount		$ 250,000,000		$ 250,000,000

Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Other property and investments	$ 31,153	$ 23,961
Total	1,305,334	834,245
Southwest Gas Corporation
Property, Plant and Equipment [Line Items]
Net cash surrender value of COLI policies	147,187	140,874
Other property and investments	2,739	2,737
Total	149,926	143,611
Centuri
Property, Plant and Equipment [Line Items]
Centuri property, equipment, and intangibles	1,592,461	1,089,414
Centuri accumulated provision for depreciation and amortization	$ (468,206)	$ (422,741)

Background, Organization, and Summary of Significant Accounting Policies - Schedule of Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 345,184
Additional goodwill from Riggs Distler acquisition	446,794
Foreign currency translation adjustment	(76)
Goodwill, ending balance	791,902
Natural Gas Operations
Goodwill [Roll Forward]
Goodwill, beginning balance	10,095
Additional goodwill from Riggs Distler acquisition	0
Foreign currency translation adjustment	0
Goodwill, ending balance	10,095
Utility Infrastructure Services
Goodwill [Roll Forward]
Goodwill, beginning balance	335,089
Additional goodwill from Riggs Distler acquisition	446,794
Foreign currency translation adjustment	(76)
Goodwill, ending balance	$ 781,807

Background, Organization, and Summary of Significant Accounting Policies - Other Income (Deductions) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other income (deductions)
Total other income (deductions)	$ (3,112)	$ 1,799	$ (3,975)	$ (11,046)	$ 282	$ (7,788)
Southwest Gas Corporation
Other income (deductions)
Total other income (deductions)	(4,287)	1,751	(4,902)	(10,947)	(545)	(7,615)
Revenues from external customers \| Natural Gas Operations \| Southwest Gas Corporation
Other income (deductions)
Change in COLI policies	0	4,500	5,800	1,000	14,000	7,200
Interest income	1,365	1,412	3,312	3,214	4,113	4,630
Equity AFUDC	0	1,232	0	3,413	1,311	4,395
Other components of net periodic benefit cost	(3,506)	(5,005)	(10,516)	(15,016)	(15,522)	(18,780)
Miscellaneous income and (expense)	(2,146)	(388)	(3,498)	(3,558)	(4,447)	(5,060)
Total other income (deductions)	(4,287)	1,751	(4,902)	(10,947)	(545)	(7,615)
Revenues from external customers \| Utility Infrastructure Services Segment \| Centuri
Other income (deductions)
Foreign transaction gain (loss)	(7)	0	(19)	(16)	(19)	(16)
Miscellaneous income and (expense)	1,182	48	946	(91)	846	(194)
Total other income (deductions)	1,175	48	927	(107)	827	(210)
Corporate and administrative
Other income (deductions)
Total other income (deductions)	$ 0	$ 0	$ 0	$ 8	$ 0	$ 37

Background, Organization, and Summary of Significant Accounting Policies - Summary of Redeemable Noncontrolling Interest (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Movement In Redeemable Noncontrolling Interest [Roll Forward]
Redeemable noncontrolling interest, beginning balance	$ 165,716
Net income attributable to redeemable noncontrolling interest	5,189
Redemption value adjustment	12,642
Redeemable noncontrolling interest, ending balance	$ 183,547

Background, Organization, and Summary of Significant Accounting Policies - Schedule of Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Weighted average basic shares (in shares)	59,688	56,271	58,639	55,683	58,209	55,508
Effect of dilutive securities:
Management Incentive Plan shares (in shares)	0	0	0	0	0	3
Restricted stock units (in shares)	128	86	103	70	103	66
Weighted average diluted shares (in shares)	59,816	56,357	58,742	55,753	58,312	55,577
Number of performance share units granted (in shares)	115	76	95	63	93	57

Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2022	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees' deferred amount				50.00%
Employer matching contribution, percent of employees' eligible annual compensation				3.50%
Forecast
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of employees' eligible annual compensation	7.00%
Employer matching contribution, percent of match (up to)	3.00%
Qualified Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 10,289	$ 8,576	$ 30,869	$ 25,725	$ 39,443	$ 32,191
Interest cost		10,108	11,388	30,324	34,165	41,714	46,416
Expected return on plan assets		(18,088)	(16,324)	(54,264)	(48,972)	(70,588)	(64,033)
Amortization of net actuarial loss		10,489	9,006	31,467	27,019	40,473	32,608
Net periodic benefit cost		12,798	12,646	38,396	37,937	51,042	47,182
SERP
Defined Benefit Plan Disclosure [Line Items]
Service cost		131	97	394	292	491	359
Interest cost		358	401	1,074	1,204	1,474	1,644
Amortization of net actuarial loss		661	451	1,981	1,353	2,433	1,608
Net periodic benefit cost		1,150	949	3,449	2,849	4,398	3,611
PBOP
Defined Benefit Plan Disclosure [Line Items]
Service cost		423	395	1,269	1,186	1,664	1,505
Interest cost		549	646	1,645	1,936	2,291	2,697
Expected return on plan assets		(810)	(852)	(2,430)	(2,556)	(3,282)	(3,345)
Amortization of prior service costs		239	289	719	867	1,007	1,185
Net periodic benefit cost		$ 401	$ 478	$ 1,203	$ 1,433	$ 1,680	$ 2,042

Revenue - Schedule of Gas Operating Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 241,300	$ 203,082	$ 1,068,164	$ 966,941	$ 1,440,374	$ 1,346,391
Alternative revenue program revenues (deferrals)	12,569	9,199	(5,335)	9,545	(2,740)	7,629
Other revenues	1,979	(1,447)	7,747	(391)	7,432	1,646
Total Gas operating revenues	255,848	210,834	1,070,576	976,095	1,445,066	1,355,666
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	147,326	131,008	743,791	690,861	1,011,450	957,379
Small commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48,283	35,204	185,774	159,122	248,193	228,720
Large commercial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14,199	9,942	40,030	32,588	52,075	45,493
Industrial/other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,608	5,888	30,352	19,089	37,505	25,435
Transportation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 21,884	$ 21,040	$ 68,217	$ 65,281	$ 91,151	$ 89,364

Revenue - Summary of Revenue Disaggregated by Service Type, and Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 241,300	$ 203,082	$ 1,068,164	$ 966,941	$ 1,440,374	$ 1,346,391
Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	632,848	580,392	1,525,448	1,408,698	2,065,038	1,877,264
Master services agreement \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	467,869	437,914	1,160,199	1,076,961	1,573,247	1,438,540
Bid contract \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	164,979	142,478	365,249	331,737	491,791	438,724
Unit price contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	406,404	377,284	1,002,779	985,673	1,373,746	1,359,352
Fixed price contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	64,632	46,379	149,681	109,935	197,447	142,356
Time and materials contracts \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	161,812	156,729	372,988	313,090	493,845	375,556
Gas infrastructure services \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	393,122	387,578	961,836	935,444	1,287,552	1,288,468
Electric power infrastructure services \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	155,456	115,386	347,061	282,992	475,895	346,432
Other \| Centuri
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 84,270	$ 77,428	$ 216,551	$ 190,262	$ 301,591	$ 242,364

Revenue - Summary of Information about Receivables (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Contracts receivable, net	$ 381,387	$ 278,316
Revenue earned on contracts in progress in excess of billings	207,318	96,996
Amounts billed in excess of revenue earned on contracts	$ 19,954	$ 4,507

Revenue - Narratives (Details) $ in Millions	9 Months Ended
Revenue - Narratives (Details) $ in Millions	Sep. 30, 2021 USD ($) Contract
Segment Reporting Information [Line Items]
Change in contract liability, revenue recognized \| $	$ 4.5
Centuri
Segment Reporting Information [Line Items]
Number of contracts with original duration more than one year \| Contract	18

Revenue - Revenue Performance Obligation (Details) - Centuri - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01 $ in Millions	Sep. 30, 2021 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Transaction price allocated to unsatisfied performance obligations of contracts	$ 53.8
Transaction price allocated to unsatisfied performance obligations of contracts, period	2 years

Revenue - Schedule of Utility Infrastructure Services Contracts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Contracts receivable, gross	$ 383,328	$ 280,470
Allowance for doubtful accounts	(1,941)	(2,154)
Contracts receivable, net	381,387	278,316
Billed on completed contracts and contracts in progress
Disaggregation of Revenue [Line Items]
Contracts receivable, gross	380,484	273,778
Other receivables
Disaggregation of Revenue [Line Items]
Contracts receivable, gross	$ 2,844	$ 6,692

Common Stock (Details) - USD ($)	3 Months Ended	6 Months Ended	9 Months Ended		12 Months Ended
Common Stock (Details) - USD ($)	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Oct. 10, 2021	Apr. 08, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Net proceeds			$ 210,812,000	$ 90,635,000	$ 259,422,000	$ 119,240,000
Common stock, par (in USD per share)	$ 1	$ 1	$ 1		$ 1				$ 1
Subsequent Event
Class of Stock [Line Items]
Number of preferred stock purchase right, per share of common stock dividend (in shares)							1
Common stock, par (in USD per share)							$ 1
Purchase price per unit (in USD per share)							$ 321.70
Preferred stock purchase price, exercisable term, beneficial ownership percentage benchmark							10.00%
Preferred stock purchase price, exercisable term, beneficial ownership percentage benchmark with passive institutional investor							20.00%
Restricted Stock/Unit Plan, and Management Incentive Plan
Class of Stock [Line Items]
Common stock issued (in shares)			47,500
Dividend Reinvestment and Stock Purchase Plan
Class of Stock [Line Items]
Common stock issued (in shares)			130,000
Common stock issued, amount			$ 8,500,000
Equity Shelf Program
Class of Stock [Line Items]
Sale of stock, amount of common stock offered for sale (up to)	$ 341,819,657	$ 341,819,657	$ 341,819,657		$ 341,819,657			$ 500,000,000
Gross proceeds	87,819,931	158,180,343
Less: agent commissions	(878,199)	(1,581,803)
Net proceeds	$ 86,941,732	$ 156,598,540
Number of shares sold (in shares)	1,251,810	2,302,407
Weighted average price per share (in USD per share)	$ 70.15	$ 68.70

Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less: current maturities	$ (297,271)		$ (40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	$ 2,309,857		2,438,206
Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.10%
Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.875%
Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%
Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.80%
Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.70%
Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.15%
Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	2.20%
Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.18%	3.18%
Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	8.00%
Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	7.78%
Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	7.92%
Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.76%
Carrying Amount
Debt Instrument [Line Items]
Less: current maturities	$ (297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(297,271)		(40,433)
Long-term debt, less current maturities	3,573,783		2,732,200
Carrying Amount \| Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(275,000)		0
Long-term debt, less current maturities	2,309,857		2,438,206
Long-term debt	2,584,857		2,438,206
Carrying Amount \| Centuri
Debt Instrument [Line Items]
Less: current maturities	(22,271)		(40,433)
Long-term debt, less current maturities	1,263,926		293,994
Unamortized debt issuance costs	(25,385)		(820)
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(22,271)		(40,433)
Long-term debt, less current maturities	1,263,926		293,994
Long-term debt	1,286,197		334,427
Centuri secured revolving credit facility	1,119,615		225,828
Carrying Amount \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	112,236		26,626
Carrying Amount \| Centuri term loan facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	1,145,000		226,648
Carrying Amount \| Centuri other debt obligations \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	54,346		81,973
Carrying Amount \| Debentures \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	2,386,773		2,089,678
Unamortized discount and debt issuance costs	(20,727)		(17,822)
Carrying Amount \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	125,000		125,000
Carrying Amount \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000		250,000
Carrying Amount \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	250,000		250,000
Carrying Amount \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		300,000
Carrying Amount \| Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	450,000		450,000
Carrying Amount \| Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	300,000		0
Carrying Amount \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	75,000		75,000
Carrying Amount \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000		25,000
Carrying Amount \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	25,000		25,000
Carrying Amount \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable	7,500		7,500
Carrying Amount \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility	0		150,000
Carrying Amount \| Industrial development revenue bonds \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(1,916)		(1,472)
Unsecured debt	198,084		198,528
Carrying Amount \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Carrying Amount \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Centuri secured revolving credit facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	112,348		26,645
Fair Value \| Centuri term loan facility \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri secured revolving credit facility	1,146,431		230,824
Fair Value \| Centuri other debt obligations \| Centuri
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	52,682		84,246
Fair Value \| Debentures \| Notes, 6.1%, due 2041 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	167,755		174,858
Fair Value \| Debentures \| Notes, 3.875%, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	252,208		258,825
Fair Value \| Debentures \| Notes, 4.875%, due 2043 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	307,385		317,190
Fair Value \| Debentures \| Notes, 3.8%, due 2046 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	326,058		347,046
Fair Value \| Debentures \| Notes, 3.7%, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	331,536		344,553
Fair Value \| Debentures \| Notes, 4.15%, due 2049 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	343,950		370,278
Fair Value \| Debentures \| Notes, 2.2%, due 2030 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	447,287		474,552
Fair Value \| Debentures \| Notes, 3.18%, due 2051 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	291,351		0
Fair Value \| Debentures \| 8% Series, due 2026 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	94,752		99,723
Fair Value \| Debentures \| Medium-term notes, 7.78% series, due 2022 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	25,513		26,663
Fair Value \| Debentures \| Medium-term notes, 7.92% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	31,936		33,802
Fair Value \| Debentures \| Medium-term notes, 6.76% series, due 2027 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Notes payable, fair value disclosure	9,116		9,613
Fair Value \| Debentures \| Revolving credit facility and commercial paper \| Southwest Gas Corporation
Debt Instrument [Line Items]
Line of credit facility, fair value	0		150,000
Fair Value \| Industrial development revenue bonds \| Tax-exempt Series A, due 2028 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2003 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2008 Series A, due 2038 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	50,000		50,000
Fair Value \| Industrial development revenue bonds \| 2009 Series A, due 2039 \| Southwest Gas Corporation
Debt Instrument [Line Items]
Unsecured debt, fair value	$ 50,000		$ 50,000

Debt - Narratives (Details)		1 Months Ended	9 Months Ended
Debt - Narratives (Details)	Nov. 01, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2023	Dec. 31, 2022	Aug. 31, 2021	Aug. 27, 2021 USD ($)	Aug. 26, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Short term borrowings outstanding			$ 272,000,000						$ 107,000,000
Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument, face amount	$ 1,600,000,000
Debt instrument, term	364 days
Change intervals of basis spread on variable rate	0.25%
Debt term, mandatory prepayment as percentage of cash proceeds received	100.00%
Debt term, percentage of committed amount under specific acquisition financings	100.00%
Minimum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Commitment fee percentage	0.06%
Maximum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Commitment fee percentage	0.175%
LIBOR \| Minimum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt, basis spread on variable rate	0.75%
LIBOR \| Maximum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt, basis spread on variable rate	1.50%
LIBOR \| Centuri term loan facility
Debt Instrument [Line Items]
Debt, basis spread on variable rate			2.50%
Term loan facility LIBOR floor			0.50%
Alternative base rate \| Minimum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt, basis spread on variable rate	0.00%
Alternative base rate \| Maximum \| Term Loan Facility \| Subsequent Event
Debt Instrument [Line Items]
Debt, basis spread on variable rate	0.50%
Alternative base rate \| Centuri term loan facility
Debt Instrument [Line Items]
Debt, basis spread on variable rate			1.50%
Southwest Gas Corporation
Debt Instrument [Line Items]
Short term borrowings outstanding			$ 250,000,000						$ 57,000,000
Southwest Gas Corporation \| $250 Million Term Loan
Debt Instrument [Line Items]
Debt instrument, face amount		$ 250,000,000
Debt covenant, ratio of funded debt to total capitalization			0.70
Debt instrument, term		364 days
Southwest Gas Corporation \| Southwest Gas Credit Facility
Debt Instrument [Line Items]
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 outstanding			0
Short term borrowings outstanding			0
Southwest Gas Corporation \| Commercial Paper Program
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			50,000,000
Borrowings outstanding under facility			$ 0
Southwest Gas Corporation \| Notes, 3.18%, due 2051 \| Debentures
Debt Instrument [Line Items]
Debt instrument interest rate			3.18%			3.18%
Debt instrument discount rate						0.019%
Southwest Gas Corporation \| LIBOR \| Minimum \| $250 Million Term Loan
Debt Instrument [Line Items]
Debt, basis spread on variable rate		0.55%
Southwest Gas Corporation \| LIBOR \| Maximum \| $250 Million Term Loan
Debt Instrument [Line Items]
Debt, basis spread on variable rate		1.00%
Southwest Gas Corporation \| LIBOR \| Southwest Gas Credit Facility
Debt Instrument [Line Items]
Debt, basis spread on variable rate			1.125%
Southwest Gas Corporation \| Alternative base rate \| $250 Million Term Loan
Debt Instrument [Line Items]
Debt, basis spread on variable rate		0.00%
Southwest Gas Corporation \| Alternative base rate \| Southwest Gas Credit Facility
Debt Instrument [Line Items]
Debt, basis spread on variable rate			0.125%
Centuri \| Secured Revolving Credit Facility and Term Loan
Debt Instrument [Line Items]
Borrowings outstanding under facility			$ 1,257,000,000
Debt secured by assets			2,600,000,000
Centuri \| Centuri term loan facility
Debt Instrument [Line Items]
Debt instrument, face amount							$ 1,145,000,000	$ 590,000,000
Centuri \| Centuri secured revolving credit facility
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity							$ 400,000,000
$400 Million Credit Facility \| Southwest Gas Corporation
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			400,000,000
$100 Million Credit Facility
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			100,000,000
Borrowings outstanding under facility			$ 22,000,000
Centuri secured revolving credit facility
Debt Instrument [Line Items]
Maximum total net leverage ratio			5.50
Increase the maximum total net leverage ratio			4.50
Minimum interest coverage ratio			2.50
Centuri secured revolving credit facility \| Forecast
Debt Instrument [Line Items]
Maximum total net leverage ratio				4.00	4.75
Centuri secured revolving credit facility \| Minimum
Debt Instrument [Line Items]
Commitment fee percentage			0.15%
Centuri secured revolving credit facility \| Maximum
Debt Instrument [Line Items]
Commitment fee percentage			0.35%
Centuri secured revolving credit facility \| LIBOR \| Minimum
Debt Instrument [Line Items]
Debt, basis spread on variable rate			1.00%
Centuri secured revolving credit facility \| LIBOR \| Maximum
Debt Instrument [Line Items]
Debt, basis spread on variable rate			2.25%
Centuri secured revolving credit facility \| Alternative base rate \| Minimum
Debt Instrument [Line Items]
Debt, basis spread on variable rate			0.00%
Centuri secured revolving credit facility \| Alternative base rate \| Maximum
Debt Instrument [Line Items]
Debt, basis spread on variable rate			1.25%
Centuri secured revolving credit facility \| Centuri
Debt Instrument [Line Items]
Debt instrument discount rate							1.00%

Other Comprehensive Income and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to OCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	$ 303	$ 3,406	$ 6,750	$ 5,571	$ (4,980)	$ (6,502)
Other comprehensive income (loss), tax	(566)	(572)	(1,698)	(1,622)	1,812	1,494
Total other comprehensive income (loss), net of tax	(263)	2,834	5,052	$ 3,949	(3,168)	(5,008)
Other comprehensive income (loss) before reclassifications, net of tax			$ (324)
Effective income tax rate			24.00%	24.00%
Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	2,359	2,382	$ 7,074	$ 6,758	(7,556)	(6,222)
Other comprehensive income (loss), tax	(566)	(572)	(1,698)	(1,622)	1,812	1,494
Total other comprehensive income (loss), net of tax	1,793	1,810	5,376	5,136	(5,744)	(4,728)
Amortization of prior service cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	239	289	719	867	1,007	1,185
Reclassification from AOCI, tax	(56)	(69)	(172)	(208)	(241)	(284)
Reclassification from AOCI, net of tax	183	220	547	659	766	901
Other comprehensive income (loss), before tax			719
Other comprehensive income (loss), tax			(172)
Total other comprehensive income (loss), net of tax			547
Amortization of prior service cost \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			719
Other comprehensive income (loss), tax			(172)
Total other comprehensive income (loss), net of tax			547
Amortization of net actuarial (gain)/loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	11,151	9,457	33,448	28,372	42,906	34,216
Reclassification from AOCI, tax	(2,677)	(2,270)	(8,028)	(6,809)	(10,298)	(8,212)
Reclassification from AOCI, net of tax	8,474	7,187	25,420	21,563	32,608	26,004
Other comprehensive income (loss), before tax			33,448
Other comprehensive income (loss), tax			(8,028)
Total other comprehensive income (loss), net of tax			25,420
Other comprehensive income (loss) before reclassifications, before tax					(57,539)	(71,087)
Other comprehensive income (loss) before reclassifications, tax					13,809	17,061
Other comprehensive income (loss) before reclassifications, net of tax					(43,730)	(54,026)
Amortization of net actuarial (gain)/loss \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			33,448
Other comprehensive income (loss), tax			(8,028)
Total other comprehensive income (loss), net of tax			25,420
Regulatory adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	(9,575)	(8,394)	(28,725)	(25,184)	3,894	27,803
Reclassification from AOCI, tax	2,298	2,014	6,894	6,044	(935)	(6,673)
Reclassification from AOCI, net of tax	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Other comprehensive income (loss), before tax			(28,725)
Other comprehensive income (loss), tax			6,894
Total other comprehensive income (loss), net of tax			(21,831)
Regulatory adjustment \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			(28,725)
Other comprehensive income (loss), tax			6,894
Total other comprehensive income (loss), net of tax			(21,831)
Prior service cost
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, before tax					0	(1,878)
Other comprehensive income (loss) before reclassifications, tax					0	452
Other comprehensive income (loss) before reclassifications, net of tax					0	(1,426)
Pension plans other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	1,815	1,352	5,442	4,055	(9,732)	(9,761)
Other comprehensive income (loss), tax	(435)	(325)	(1,306)	(973)	2,335	2,344
Total other comprehensive income (loss), net of tax	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Pension plans other comprehensive income (loss) \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax			5,442
Other comprehensive income (loss), tax			(1,306)
Total other comprehensive income (loss), net of tax			4,136
FSIRS
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	544	1,030	1,632	2,703	2,176	3,539
Reclassification from AOCI, tax	(131)	(247)	(392)	(649)	(523)	(850)
Reclassification from AOCI, net of tax	413	783	1,240	2,054	1,653	2,689
Other comprehensive income (loss), before tax	544	1,030	1,632	2,703	2,176	3,539
Other comprehensive income (loss), tax	(131)	(247)	(392)	(649)	(523)	(850)
Total other comprehensive income (loss), net of tax	413	783	1,240	2,054	1,653	2,689
FSIRS \| Southwest Gas Corporation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax			1,632
Reclassification from AOCI, tax			(392)
Reclassification from AOCI, net of tax			1,240
Other comprehensive income (loss), before tax			1,632
Other comprehensive income (loss), tax			(392)
Total other comprehensive income (loss), net of tax			1,240
Foreign currency items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassifications, before tax	(2,056)	1,024	(324)	(1,187)	2,576	(280)
Other comprehensive income (loss) before reclassifications, tax	0	0	0	0	0	0
Other comprehensive income (loss) before reclassifications, net of tax	$ (2,056)	$ 1,024	$ (324)	$ (1,187)	$ 2,576	$ (280)

Other Comprehensive Income and Accumulated Other Comprehensive Income - Additional Information (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Equity [Abstract]
Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months	$ 828

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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent			$ 2,674,953
Other comprehensive income (loss) before reclassifications, net of tax			(324)
Other comprehensive income (loss), before tax	$ 303	$ 3,406	6,750	$ 5,571	$ (4,980)	$ (6,502)
Other comprehensive income (loss), tax	(566)	(572)	(1,698)	(1,622)	1,812	1,494
Total other comprehensive income (loss), net of tax	(263)	2,834	5,052	$ 3,949	(3,168)	(5,008)
Ending balance, attributable to parent	2,909,816		$ 2,909,816		2,909,816
Effective income tax rate			24.00%	24.00%
Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			$ (77,720)
Beginning balance, tax			18,653
Beginning balance			(59,067)
Other comprehensive income (loss), before tax	1,815	1,352	5,442	$ 4,055	(9,732)	(9,761)
Other comprehensive income (loss), tax	(435)	(325)	(1,306)	(973)	2,335	2,344
Total other comprehensive income (loss), net of tax	1,380	1,027	4,136	3,082	(7,397)	(7,417)
Ending balance, before tax	(72,278)		(72,278)		(72,278)
Ending balance, tax	17,347		17,347		17,347
Ending balance	(54,931)		(54,931)		(54,931)
Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	239	289	719	867	1,007	1,185
Reclassification from AOCI, tax	(56)	(69)	(172)	(208)	(241)	(284)
Reclassification from AOCI, net of tax	183	220	547	659	766	901
Other comprehensive income (loss), before tax			719
Other comprehensive income (loss), tax			(172)
Total other comprehensive income (loss), net of tax			547
Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, before tax					(57,539)	(71,087)
Other comprehensive income (loss) before reclassifications, net of tax					(43,730)	(54,026)
Reclassification from AOCI, before Tax	11,151	9,457	33,448	28,372	42,906	34,216
Reclassification from AOCI, tax	(2,677)	(2,270)	(8,028)	(6,809)	(10,298)	(8,212)
Reclassification from AOCI, net of tax	8,474	7,187	25,420	21,563	32,608	26,004
Other comprehensive income (loss), before tax			33,448
Other comprehensive income (loss), tax			(8,028)
Total other comprehensive income (loss), net of tax			25,420
Regulatory adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, before Tax	(9,575)	(8,394)	(28,725)	(25,184)	3,894	27,803
Reclassification from AOCI, tax	2,298	2,014	6,894	6,044	(935)	(6,673)
Reclassification from AOCI, net of tax	(7,277)	(6,380)	(21,831)	(19,140)	2,959	21,130
Other comprehensive income (loss), before tax			(28,725)
Other comprehensive income (loss), tax			6,894
Total other comprehensive income (loss), net of tax			(21,831)
FSIRS
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			(2,719)
Beginning balance, tax			651
Beginning balance			(2,068)
Reclassification from AOCI, before Tax	544	1,030	1,632	2,703	2,176	3,539
Reclassification from AOCI, tax	(131)	(247)	(392)	(649)	(523)	(850)
Reclassification from AOCI, net of tax	413	783	1,240	2,054	1,653	2,689
Other comprehensive income (loss), before tax	544	1,030	1,632	2,703	2,176	3,539
Other comprehensive income (loss), tax	(131)	(247)	(392)	(649)	(523)	(850)
Total other comprehensive income (loss), net of tax	413	783	1,240	2,054	1,653	2,689
Ending balance, before tax	(1,087)		(1,087)		(1,087)
Ending balance, tax	259		259		259
Ending balance	(828)		(828)		(828)
Foreign Currency Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, before tax			132
Beginning balance			132
Other comprehensive income (loss) before reclassifications, before tax			(324)
Other comprehensive income (loss) before reclassifications, net of tax			(324)
Ending balance, before tax	(192)		(192)		(192)
Ending balance	(192)		(192)		(192)
AOCI Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, net of tax			5,052
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(55,688)	(55,617)	(61,003)	(56,732)	(52,783)
Ending balance	(55,951)	(52,783)	(55,951)	(52,783)	(55,951)	(52,783)
Southwest Gas Corporation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance					2,144,273
Beginning balance, attributable to parent			2,233,468
Other comprehensive income (loss), before tax	2,359	2,382	7,074	6,758	(7,556)	(6,222)
Other comprehensive income (loss), tax	(566)	(572)	(1,698)	(1,622)	1,812	1,494
Total other comprehensive income (loss), net of tax	1,793	1,810	5,376	5,136	(5,744)	(4,728)
Ending balance, attributable to parent	2,462,794		2,462,794		2,462,794
Ending balance	2,462,794	2,144,273	2,462,794	2,144,273	2,462,794	2,144,273
Southwest Gas Corporation \| Defined Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent, before tax			(77,720)
Beginning balance, attributable to parent, tax			18,653
Beginning balance, attributable to parent			(59,067)
Other comprehensive income (loss), before tax			5,442
Other comprehensive income (loss), tax			(1,306)
Total other comprehensive income (loss), net of tax			4,136
Ending balance, attributable to parent, before tax	(72,278)		(72,278)		(72,278)
Ending balance, attributable to parent, tax	17,347		17,347		17,347
Ending balance, attributable to parent	(54,931)		(54,931)		(54,931)
Southwest Gas Corporation \| Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			719
Other comprehensive income (loss), tax			(172)
Total other comprehensive income (loss), net of tax			547
Southwest Gas Corporation \| Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			33,448
Other comprehensive income (loss), tax			(8,028)
Total other comprehensive income (loss), net of tax			25,420
Southwest Gas Corporation \| Regulatory adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before tax			(28,725)
Other comprehensive income (loss), tax			6,894
Total other comprehensive income (loss), net of tax			(21,831)
Southwest Gas Corporation \| FSIRS
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, attributable to parent, before tax			(2,719)
Beginning balance, attributable to parent, tax			651
Beginning balance, attributable to parent			(2,068)
Reclassification from AOCI, before Tax			1,632
Reclassification from AOCI, tax			(392)
Reclassification from AOCI, net of tax			1,240
Other comprehensive income (loss), before tax			1,632
Other comprehensive income (loss), tax			(392)
Total other comprehensive income (loss), net of tax			1,240
Ending balance, attributable to parent, before tax	(1,087)		(1,087)		(1,087)
Ending balance, attributable to parent, tax	259		259		259
Ending balance, attributable to parent	(828)		(828)		(828)
Southwest Gas Corporation \| AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(57,552)	(51,825)	(61,135)	(55,151)	(50,015)
Beginning balance, attributable to parent			(61,135)
Ending balance, attributable to parent	(55,759)		(55,759)		(55,759)
Ending balance	$ (55,759)	$ (50,015)	$ (55,759)	$ (50,015)	$ (55,759)	$ (50,015)

Other Comprehensive Income and Accumulated Other Comprehensive Income - Amounts Recognized Before Tax, Defined Benefit Plans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Equity [Abstract]
Net actuarial loss	$ (469,335)	$ (502,783)
Prior service cost	(1,768)	(2,487)
Less: amount recognized in regulatory assets	398,825	427,550
Recognized in AOCI	$ (72,278)	$ (77,720)

Segment Information - Narratives (Details)	9 Months Ended
Segment Information - Narratives (Details)	Sep. 30, 2021 segment
Segment Reporting Information [Line Items]
Number of reportable segments	2
Southwest Gas Corporation
Segment Reporting Information [Line Items]
Number of reportable segments	1

Segment Information - Accounts Receivable for Services (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Centuri
Segment Reporting Information [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 15,376	$ 13,956

- Definition

The aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. which are usually due within one year (or one business cycle).

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+ Details

Segment Information - Utility Infrastructure Services Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 10,369,635	$ 8,735,853
Utility Infrastructure Services \| Centuri
Segment Reporting Information [Line Items]
Assets	$ 2,671,974	$ 1,475,237

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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+ Details

Segment Information - Schedule of Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 888,696	$ 791,226	$ 2,596,024	$ 2,384,793	$ 3,510,104	$ 3,232,930
Segment net income (loss)	(11,576)	18,273	130,836	128,780	234,380	220,498
Revenues from external customers
Segment Reporting Information [Line Items]
Revenues	861,854	759,134	2,521,295	2,282,576	3,402,733	3,094,096
Intersegment revenues
Segment Reporting Information [Line Items]
Revenues	26,842	32,092	74,729	102,217	107,371	138,834
Segment net income (loss)	(2,572)	(627)	(4,545)	(1,724)	(4,477)	(2,110)
Natural Gas Operations
Segment Reporting Information [Line Items]
Revenues	255,848	210,834	1,070,576	976,095	1,445,066	1,355,666
Segment net income (loss)	(27,544)	(15,973)	102,584	79,568	182,134	155,993
Natural Gas Operations \| Revenues from external customers
Segment Reporting Information [Line Items]
Revenues	255,848	210,834	1,070,576	976,095	1,445,066	1,355,666
Natural Gas Operations \| Intersegment revenues
Segment Reporting Information [Line Items]
Revenues	0	0	0	0	0	0
Utility Infrastructure Services
Segment Reporting Information [Line Items]
Revenues	632,848	580,392	1,525,448	1,408,698	2,065,038	1,877,264
Segment net income (loss)	18,540	34,873	32,797	50,936	56,723	66,615
Utility Infrastructure Services \| Revenues from external customers
Segment Reporting Information [Line Items]
Revenues	606,006	548,300	1,450,719	1,306,481	1,957,667	1,738,430
Utility Infrastructure Services \| Intersegment revenues
Segment Reporting Information [Line Items]
Revenues	$ 26,842	$ 32,092	$ 74,729	$ 102,217	$ 107,371	$ 138,834

- Definition

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

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+ Details

Business Acquisitions - Narrative (Detail) - Drum Parent, Inc. - USD ($) $ in Millions		3 Months Ended	9 Months Ended
	Aug. 27, 2021	Sep. 30, 2021	Sep. 30, 2021
Business Acquisition [Line Items]
Gross contractual receivable	$ 81.0
Contractual receivables deemed uncollectible	12.0
Incurred and expensed acquisition costs	14.0
Acquisition-related costs		$ 13.2	$ 14.0
Goodwill tax-deductible amount	76.0
Centuri
Business Acquisition [Line Items]
Payments to acquire business	$ 830.4

Business Acquisitions - Summary of Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 27, 2021	Dec. 31, 2020
Fair Values of Assets Acquired and Liabilities Assumed
Goodwill	$ 791,902		$ 345,184
Drum Parent, Inc.
Fair Values of Assets Acquired and Liabilities Assumed
Cash and cash equivalents		$ 1,900
Accounts receivable		69,100
Contract assets		40,100
Income taxes receivable, net		700
Right of use assets under operating leases		1,500
Prepaid expenses		5,200
Property and equipment		118,100
Intangible assets		335,000
Goodwill		446,800
Total assets acquired		1,018,400
Trade and other payables		46,200
Finance lease obligations		27,500
Contract liabilities		12,700
Operating lease obligations		1,500
Other liabilities		5,300
Deferred tax liabilities		94,800
Total liabilities assumed		188,000
Net assets acquired		$ 830,400

Business Acquisitions - Major Classes of Intangible Assets Acquired (Details) - Drum Parent, Inc. $ in Millions	Aug. 27, 2021 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair Value	$ 335
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair Value	$ 5
Estimated Weighted Average Useful Life in Years	1 year
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair Value	$ 60
Estimated Weighted Average Useful Life in Years	15 years
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair Value	$ 270
Estimated Weighted Average Useful Life in Years	19 years

Business Acquisitions - Schedule of Pro Forma Consolidated Financial Information (Details) - Drum Parent, Inc. - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Business acquisition, pro forma adjustment, transaction costs			$ 30,000
Business acquisition, pro forma adjustment, transaction costs, incremental interest expense of new loan facility	$ 7,000	$ 9,000	27,000	$ 24,500
Total operating revenues	956,120	907,512	2,903,658	2,702,062
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (8,918)	$ 12,688	$ 120,828	$ 84,049
Basic earnings per share (in USD per Share)	$ (0.15)	$ 0.23	$ 2.06	$ 1.51
Diluted earnings per share (in USD per Share)	$ (0.15)	$ 0.23	$ 2.06	$ 1.51

Business Acquisitions - Schedule of Actual Results from Operations for Acquiree (Details) - Drum Parent, Inc. $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Business Acquisition [Line Items]
Utility infrastructure services revenues	$ 49,520
Net income attributable to Southwest Gas Holdings, Inc.	$ 1,646