View Filing Data

Print Document View Excel Document

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2017	Apr. 28, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q1
Trading Symbol	SWX
Entity Registrant Name	SOUTHWEST GAS HOLDINGS, INC.
Entity Central Index Key	0001692115
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		47,559,471

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Utility plant:
Gas plant	$ 6,280,654	$ 6,193,564
Less: accumulated depreciation	(2,194,660)	(2,172,966)
Acquisition adjustments, net	158	196
Construction work in progress	91,428	111,177
Net utility plant	4,177,580	4,131,971
Other property and investments	351,032	342,343
Current assets:
Cash and cash equivalents	43,401	28,066
Accounts receivable, net of allowances	247,179	285,145
Accrued utility revenue	45,900	76,200
Income taxes receivable, net	4,512	4,455
Deferred purchased gas costs	9,142	2,608
Prepaids and other current assets	104,270	136,833
Total current assets	454,404	533,307
Noncurrent assets:
Goodwill	140,974	139,983
Deferred income taxes	1,323	1,288
Deferred charges and other assets	426,600	432,234
Total noncurrent assets	568,897	573,505
Total assets	5,551,913	5,581,126
Capitalization:
Common stock	49,179	49,112
Additional paid-in capital	909,362	903,123
Accumulated other comprehensive income (loss), net	(46,682)	(48,008)
Retained earnings	803,522	759,263
Total Southwest Gas Holdings, Inc./Total Southwest Gas Corporation equity	1,715,381	1,663,490
Noncontrolling interest	(2,262)	(2,217)
Total equity	1,713,119	1,661,273
Redeemable noncontrolling interest	23,525	22,590
Long-term debt, less current maturities	1,564,132	1,549,983
Total capitalization	3,300,776	3,233,846
Current liabilities:
Current maturities of long-term debt	26,064	50,101
Accounts payable	134,238	184,669
Customer deposits	72,227	72,296
Income taxes payable		1,909
Accrued general taxes	62,790	42,921
Accrued interest	24,876	17,939
Deferred purchased gas costs	27,104	90,476
Other current liabilities	149,529	168,064
Total current liabilities	496,828	628,375
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	879,631	840,653
Accumulated removal costs	309,000	308,000
Other deferred credits and other long-term liabilities	565,678	570,252
Total deferred income taxes and other credits	1,754,309	1,718,905
Total capitalization and liabilities	5,551,913	5,581,126
Southwest Gas Corporation [Member]
Utility plant:
Gas plant	6,280,654	6,193,564
Less: accumulated depreciation	(2,194,660)	(2,172,966)
Acquisition adjustments, net	158	196
Construction work in progress	91,428	111,177
Net utility plant	4,177,580	4,131,971
Other property and investments	111,396	108,569
Current assets:
Cash and cash equivalents	30,950	19,024
Accounts receivable, net of allowances	118,917	111,845
Accrued utility revenue	45,900	76,200
Income taxes receivable, net	1,665	4,455
Deferred purchased gas costs	9,142	2,608
Receivable from parent	1,135
Prepaids and other current assets	94,817	126,363
Total current assets	302,526	340,495
Noncurrent assets:
Goodwill	10,095	10,095
Deferred charges and other assets	405,294	410,625
Discontinued operations - construction services - assets		579,371
Total noncurrent assets	415,389	1,000,091
Total assets	5,006,891	5,581,126
Capitalization:
Common stock	49,112	49,112
Additional paid-in capital	903,252	897,346
Accumulated other comprehensive income (loss), net	(44,526)	(45,639)
Retained earnings	642,501	767,061
Total Southwest Gas Holdings, Inc./Total Southwest Gas Corporation equity	1,550,339	1,667,880
Discontinued operations - construction services non-owner equity		15,983
Total equity	1,550,339	1,667,880
Long-term debt, less current maturities	1,385,315	1,375,080
Total capitalization	2,935,654	3,058,943
Current liabilities:
Current maturities of long-term debt		25,000
Accounts payable	93,494	138,229
Customer deposits	72,227	72,296
Accrued general taxes	62,790	42,921
Accrued interest	24,340	17,395
Deferred purchased gas costs	27,104	90,476
Payable to parent	22,734
Other current liabilities	73,550	95,999
Total current liabilities	376,239	482,316
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	846,918	806,109
Accumulated removal costs	309,000	308,000
Other deferred credits and other long-term liabilities	539,080	545,143
Discontinued operations - construction services - liabilities		380,615
Total deferred income taxes and other credits	1,694,998	2,039,867
Total capitalization and liabilities	$ 5,006,891	$ 5,581,126

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par	$ 1	$ 1
Common stock, authorized	60,000,000	60,000,000
Common stock, issued	47,548,985	47,482,068
Common stock, outstanding	47,548,985	47,482,068

Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Operating revenues:
Gas operating revenues	$ 462,602	$ 525,100	$ 1,258,914	$ 1,426,624
Construction revenues	192,135	206,148	1,125,065	1,034,029
Total operating revenues	654,737	731,248	2,383,979	2,460,653
Gas operating revenues	462,602	525,100	1,258,914	1,426,624
Operating expenses:
Net cost of gas sold	146,879	213,600	330,400	523,647
Operations and maintenance	109,150	100,797	410,077	398,486
Depreciation and amortization	72,478	75,360	286,250	278,004
Taxes other than income taxes	14,782	14,013	53,145	50,409
Construction expenses	191,956	193,382	1,022,997	917,235
Total operating expenses	535,245	597,152	2,102,869	2,167,781
Operating income	119,492	134,096	281,110	292,872
Other income and (expenses):
Net interest deductions	(18,714)	(17,721)	(74,653)	(71,623)
Other income (deductions)	3,865	1,721	11,613	2,328
Total other income and (expenses)	(14,849)	(16,000)	(63,040)	(69,295)
Income (loss) before income taxes	104,643	118,096	218,070	223,577
Income tax expense	35,638	42,741	71,365	80,671
Net income	69,005	75,355	146,705	142,906
Net income (loss) attributable to noncontrolling interests	(303)	(91)	802	1,126
Net income (loss)	$ 69,308	$ 75,446	$ 145,903	$ 141,780
Basic earnings per share	$ 1.46	$ 1.59	$ 3.07	$ 3.00
Diluted earnings per share	1.45	1.58	3.05	2.98
Dividends declared per share	$ 0.495	$ 0.450	$ 1.845	$ 1.665
Average number of common shares outstanding	47,530	47,437	47,492	47,196
Average shares outstanding (assuming dilution)	47,864	47,763	47,839	47,562
Southwest Gas Corporation [Member]
Operating revenues:
Gas operating revenues	$ 462,602	$ 525,100	$ 1,258,914	$ 1,426,624
Gas operating revenues	462,602	525,100	1,258,914	1,426,624
Operating expenses:
Net cost of gas sold	146,879	213,600	330,400	523,647
Operations and maintenance	108,679	100,797	409,606	398,486
Depreciation and amortization	61,195	60,745	233,913	220,525
Taxes other than income taxes	14,782	14,013	53,145	50,409
Total operating expenses	331,535	389,155	1,027,064	1,193,067
Operating income	131,067	135,945	231,850	233,557
Other income and (expenses):
Net interest deductions	(17,210)	(16,230)	(67,977)	(64,229)
Other income (deductions)	3,611	1,755	10,132	1,445
Total other income and (expenses)	(13,599)	(14,475)	(57,845)	(62,784)
Income (loss) before income taxes	117,468	121,470	174,005	170,773
Income tax expense	40,530	43,887	55,227	60,486
Net income	76,938	77,583	118,778	110,287
Discontinued operations - construction services, income (loss) before income taxes		(3,374)	56,890	52,804
Discontinued operations - construction services, Income tax expense (benefit)		(1,146)	21,030	20,185
Discontinued operations - construction services, Income (loss)		(2,228)	35,860	32,619
Discontinued Operations - Construction services - Noncontrolling interests		(91)	1,105	1,126
Income (loss) - discontinued operations		(2,137)	34,755	31,493
Net income (loss)	$ 76,938	$ 75,446	$ 153,533	$ 141,780

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Net income	$ 69,005	$ 75,355	$ 146,705	$ 142,906
Defined benefit pension plans:
Net actuarial gain (loss)			(14,118)	(18,922)
Amortization of prior service cost	207	207	828	829
Amortization of net actuarial loss	3,944	4,196	16,529	20,182
Regulatory adjustment	(3,556)	(3,796)	(3,222)	(2,468)
Net defined benefit pension plans	595	607	17	(379)
Forward-starting interest rate swaps:
Amounts reclassified into net income	518	519	2,074	2,073
Net forward-starting interest rate swaps	518	519	2,074	2,073
Foreign currency translation adjustments	220	782	(401)	100
Total other comprehensive income (loss), net of tax	1,333	1,908	1,690	1,794
Comprehensive income	70,338	77,263	148,395	144,700
Comprehensive income (loss) attributable to noncontrolling interests	(296)	(65)	788	1,129
Comprehensive income	70,634	77,328	147,607	143,571
Southwest Gas Corporation [Member]
Net income	76,938	77,583	118,778	110,287
Defined benefit pension plans:
Net actuarial gain (loss)			(14,118)	(18,922)
Amortization of prior service cost	207	207	828	829
Amortization of net actuarial loss	3,944	4,196	16,529	20,182
Regulatory adjustment	(3,556)	(3,796)	(3,222)	(2,468)
Net defined benefit pension plans	595	607	17	(379)
Forward-starting interest rate swaps:
Amounts reclassified into net income	518	519	2,074	2,073
Net forward-starting interest rate swaps	518	519	2,074	2,073
Total other comprehensive income (loss), net of tax	1,113	1,126	2,091	1,694
Comprehensive income	78,051	78,709	120,869	111,981
Discontinued operations - construction services, net income (loss)		(2,137)	34,755	31,493
Discontinued operations - construction services, foreign currency translation adjustments		782	(621)	100
Discontinued operations - construction services, comprehensive income (loss),		(1,355)	34,134	31,593
Discontinued operations - construction services, comprehensive income (loss) attributable to noncontrolling interests		26	(21)	3
Comprehensive income (loss) attributable to discontinued operations - construction services		(1,381)	34,155	31,590
Comprehensive income	$ 78,051	$ 77,328	$ 155,024	$ 143,571

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 69,005	$ 75,355	$ 146,705	$ 142,906
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	72,478	75,360	286,250	278,004
Deferred income taxes	37,245	18,931	87,046	60,132
Changes in current assets and liabilities:
Accounts receivable, net of allowances	36,889	45,525	21,460	37,525
Accrued utility revenue	30,300	29,600	(800)	(700)
Deferred purchased gas costs	(69,906)	58,977	(83,025)	129,120
Accounts payable	(55,298)	(35,126)	1,523	10,556
Accrued taxes	20,397	38,196	10,660	(18,118)
Other current assets and liabilities	21,099	6,776	(15,228)	(6,472)
Gains on sale	(339)	(1,333)	(6,154)	(2,909)
Changes in undistributed stock compensation	6,111	1,394	10,173	3,846
AFUDC	(475)	(532)	(2,232)	(3,144)
Changes in other assets and deferred charges	(7,173)	(291)	10,078	(1,121)
Changes in other liabilities and deferred credits	1,510	1,719	(18,656)	11,706
Net cash provided by operating activities	161,843	314,551	447,800	641,331
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(115,790)	(112,561)	(532,760)	(510,170)
Acquisition of businesses, net of cash acquired			(17,000)
Restricted cash				785
Changes in customer advances	1,057	3,661	5,296	16,515
Miscellaneous inflows	4,721	1,126	16,634	6,645
Net cash used in investing activities	(110,012)	(107,774)	(527,830)	(486,225)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net		401	71	27,006
Dividends paid	(21,397)	(19,220)	(85,494)	(76,445)
Centuri distribution to redeemable noncontrolling interest	(102)	(99)	(442)	(198)
Issuance of long-term debt, net	26,280	49,375	400,851	134,896
Retirement of long-term debt	(47,763)	(42,312)	(260,724)	(212,203)
Change in credit facility and commercial paper	10,000	(150,000)	15,000
Change in short-term debt		(18,000)
Principal payments on capital lease obligations	(199)	(313)	(1,240)	(1,347)
Withholding remittance - share-based compensation	(2,518)	(1,898)	(2,739)	(3,771)
Other	(913)	142	(2,624)	512
Net cash provided by (used in) financing activities	(36,612)	(181,924)	62,659	(131,550)
Effects of currency translation on cash and cash equivalents	116	(41)	(37)	(760)
Change in cash and cash equivalents	15,335	24,812	(17,408)	22,796
Cash and cash equivalents at beginning of period	28,066	35,997	60,809	38,013
Cash and cash equivalents at end of period	43,401	60,809	43,401	60,809
Supplemental information:
Interest paid, net of amounts capitalized	10,288	10,593	67,135	66,719
Income taxes paid	1,827	2,136	(19,341)	43,260
Southwest Gas Corporation [Member]
CASH FLOW FROM OPERATING ACTIVITIES:
Net Income	76,938	75,355	154,638	142,906
Net income	76,938	77,583	118,778	110,287
Income (loss) from discontinued operations		(2,228)	35,860	32,619
Income from continuing operations	76,938	77,583	118,778	110,287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	61,195	60,745	233,913	220,525
Deferred income taxes	39,223	19,453	87,729	62,733
Changes in current assets and liabilities:
Accounts receivable, net of allowances	(7,072)	27,909	5,750	25,724
Accrued utility revenue	30,300	29,600	(800)	(700)
Deferred purchased gas costs	(69,906)	58,977	(83,025)	129,120
Accounts payable	(44,736)	(32,324)	3,771	1,578
Accrued taxes	25,176	36,049	10,637	(18,047)
Other current assets and liabilities	37,342	8,404	(6,677)	(5,400)
Changes in undistributed stock compensation	5,711	1,394	9,773	3,846
AFUDC	(475)	(532)	(2,232)	(3,144)
Changes in other assets and deferred charges	(7,261)	(378)	9,728	(1,641)
Changes in other liabilities and deferred credits	1,198	1,719	(18,968)	11,706
Net cash provided by operating activities	147,633	288,599	368,377	536,587
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(101,007)	(89,713)	(468,413)	(444,494)
Changes in customer advances	1,057	3,661	5,296	16,515
Miscellaneous inflows	784	711	3,055	3,325
Dividends received		2,801	9,660	5,602
Net cash used in investing activities	(99,166)	(82,540)	(450,402)	(419,052)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net		401	71	27,006
Dividends paid	(18,500)	(19,220)	(82,597)	(76,445)
Issuance of long-term debt, net			296,469
Retirement of long-term debt	(25,000)		(149,855)	(51,200)
Change in credit facility and commercial paper	10,000	(150,000)	15,000
Change in short-term debt		(18,000)
Withholding remittance - share-based compensation	(2,518)	(1,898)	(2,739)	(3,771)
Other	(523)	142	(2,234)	563
Net cash provided by (used in) financing activities	(36,541)	(188,575)	74,115	(103,847)
Net cash provided by discontinued operating activities		25,952	65,213	104,744
Net cash used in discontinued investing activities		(25,234)	(66,582)	(67,173)
Net cash provided by (used in) discontinued financing activities		6,651	(11,385)	(27,703)
Effects of currency translation on cash and cash equivalents		(41)	(153)	(760)
Change in cash and cash equivalents	11,926	24,812	(20,817)	22,796
Change in cash and cash equivalents of discontinued operations included in discontinued operations construction services assets		(7,328)	12,907	(9,108)
Change in cash and cash equivalents of continuing operations	11,926	17,484	(7,910)	13,688
Cash and cash equivalents at beginning of period	19,024	21,376	38,860	25,172
Cash and cash equivalents at end of period	30,950	38,860	30,950	38,860
Supplemental information:
Interest paid, net of amounts capitalized	8,989	9,278	61,212	59,515
Income taxes paid (received)	$ (38)	$ 5,718	$ (36,767)	$ 21,437

Nature of Operations and Basis of Presentation

3 Months Ended

Mar. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Operations and Basis of Presentation

Note 1 – Nature of Operations and Basis of Presentation

Nature of Operations. Southwest Gas Holdings, Inc. is a holding company, owning all of the shares of common stock of Southwest Gas Corporation and 96.6% of the common stock of Centuri Construction Group Inc. In January 2017, a previously contemplated and approved reorganization under a holding company structure was made effective. The reorganization is designed to provide further separation between regulated and unregulated businesses, and to provide additional financing flexibility. Coincident with the effective date of the reorganization, existing shareholders of Southwest Gas Corporation became shareholders of Southwest Gas Holdings, Inc., on a one-for-one basis, with the same number of shares and same ownership percentage as they held immediately prior to the reorganization. At the same time, Southwest Gas Corporation and Centuri Construction Group Inc. (“Centuri” or the “construction services” segment) each became subsidiaries of the publicly traded holding company; whereas, historically, Centuri had been a direct subsidiary of Southwest Gas Corporation. Southwest Gas Corporation (“Southwest” or the “natural gas operations segment”) 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 construction services enterprise dedicated to meeting the growing demands of North American utilities, energy and industrial markets. Centuri derives revenue from installation, replacement, repair, and maintenance of energy distribution systems, and developing industrial construction solutions primarily for energy services utilities. Centuri operations are generally conducted under the business names of NPL Construction Co. (“NPL”), NPL Canada Ltd. (“NPL Canada”, formerly Link-Line Contractors Ltd.), W.S. Nicholls Construction, Inc. and related companies (“W.S. Nicholls”), and Brigadier Pipelines Inc. (“Brigadier”). Typically, Centuri revenues are lowest during the first quarter of the year due to unfavorable winter weather conditions. Operating revenues typically improve as more favorable weather conditions occur during the summer and fall months.

Basis of Presentation. The condensed consolidated financial statements for Southwest Gas Holdings, Inc. and subsidiaries (the “Company”) and Southwest included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with United States generally accepted accounting principles (“U.S. GAAP”) have been condensed or omitted pursuant to such rules and regulations. As indicated above, in connection with the holding company reorganization, Centuri ceased to be a subsidiary of Southwest and became a subsidiary Southwest Gas Holdings, Inc. To give effect to this change, the separate condensed consolidated financial statements related to Southwest Gas Corporation, which are included in this Form 10-Q, depict Centuri-related amounts for periods prior to January 1, 2017 as discontinued operations. Because the transfer of Centuri from Southwest Gas Corporation to Southwest Gas Holdings, Inc. was effectuated as an equity transaction and not a sale, assets and liabilities subject to the discontinued operations presentation have been reflected as noncurrent on the Southwest Gas Corporation Balance Sheet. Those assets and liabilities are detailed in Note 10 – Reorganization Impacts – Discontinued Operations Solely Related to Southwest Gas Corporation, and include both current and non-current amounts.

No substantive change has occurred with regard to the Company’s business segments on the whole, or in the primary businesses comprising those segments. Centuri operations continue to be part of continuing operations and of the consolidated financial statements of Southwest Gas Holdings, Inc.

The preparation of the condensed consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of management, all adjustments, consisting of normal recurring items and estimates necessary for a fair presentation of results for the interim periods, have been made. It is suggested that these condensed consolidated financial statements be read in conjunction with the consolidated financial statements and the notes thereto included in the 2016 Annual Report to Shareholders, which is incorporated by reference into the 2016 Form 10-K.

Prepaids and other current assets. Prepaids and other current assets includes gas pipe materials and operating supplies of $35 million at March 31, 2017 and $30 million at December 31, 2016 (carried at weighted average cost), and also includes natural gas stored underground and liquefied natural gas, in addition to prepaid assets.

Cash and Cash Equivalents. For purposes of reporting consolidated cash flows, cash and cash equivalents include cash on hand and financial instruments with a purchase-date maturity of three months or less. In general, cash and cash equivalents fall within Level 1 (quoted prices for identical financial instruments) of the three-level fair value hierarchy that ranks the inputs, used to measure fair value, by their reliability. However, cash and cash equivalents at March 31, 2017 and December 31, 2016 also include a money market fund investment of approximately $14.1 million and $5.3 million, respectively, which falls within Level 2 (significant other observable inputs) of the fair value hierarchy, due to the asset valuation methods used by money market funds.

Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $477,000 and $900,000, during the first three months of 2017 and 2016, respectively, were applied as contributions toward utility construction activity and represent non-cash investing activity.

Adoption of Accounting Standards Update (“ASU”) No. 2016-09. As of January 1, 2017, the Company adopted Financial Accounting Standards Board (“FASB”) ASU No. 2016-09 “Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting”. The adoption of this update is considered a change in accounting principle. Among other things, the update clarifies that all cash payments made to taxing authorities on the employees’ behalf for withheld shares should be presented as financing activities on the statement of cash flows. This change is required to be presented in the cash flow statement retrospectively. A new category, Withholding remittance – share-based compensation has been added to the Cash Flow from Financing Activities section of the Condensed Consolidated Statements of Cash Flows for both Southwest Gas Holdings, Inc. and Southwest Gas Corporation. The withheld taxes were included in the Accrued taxes line item of the Condensed Consolidated Statement of Cash Flows in previous periods. Therefore, upon adoption, amounts presented as cash inflows from Accrued taxes under the Cash Flow from Operating Activities section of the Southwest Gas Holdings, Inc. Consolidated Cash Flow Statements were revised from $36.3 million to $38.2 million for the three months ended March 31, 2016 and outflows in the same category for the twelve months ended March 31, 2016 were revised from $21.9 million to $18.1 million. In addition, while standalone financial statements were not previously presented for natural gas operations, for reasons related to the holding company reorganization discussed above, they are being presented commencing with this Form 10-Q. Therefore, upon adoption of this standard, the Cash Flow from Operating Activities section of the Southwest Gas Corporation Cash Flow Statements reflect a restatement of cash inflows from Accrued taxes from $34.2 million to $36 million for the three months ended March 31, 2016 and cash outflows in the same category were revised from $21.8 million to $18 million for the twelve months ended March 31, 2016.

Under the new guidance, the Company can withhold any amount between the minimum and maximum individual statutory tax rates and still treat the entire award as equity. The Company intends to administer withholding such that awards under stock compensation programs will continue to be treated as equity awards.

In addition to the above, the update requires all income tax-related cash flows resulting from share-based payments (unrelated to employee withholding) be reported as operating activities on the statement of cash flows, a change from the current requirement to present windfall tax benefits as an inflow from financing activities and an outflow from operating activities. The Company chose to apply this presentation requirement of the update prospectively as permitted. Therefore, prior periods were not impacted in implementing this provision of the update.

Amendments related to the timing of when excess tax benefits are recognized, minimum statutory withholding requirements, forfeitures, and intrinsic value are required to be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. The Company had no previously unrecognized tax benefits as a result of these changes; therefore, no cumulative effect adjustment to the Company’s opening retained earnings was required.

Goodwill. Goodwill is assessed each October for impairment (required annually by U.S. GAAP), or otherwise, if circumstances indicate impairment to the carrying value of goodwill may have occurred. In consideration of the holding company reorganization, management of the Company considered its reporting units and segments and determined that historic judgments regarding its segments and reporting units continue to apply, and that no change was necessary with regard to the level at which goodwill is assessed for impairment. No impairment was deemed to have occurred in the first three months of 2017.


(In thousands of dollars)	Natural Gas Operations		Construction Services		Consolidated
December 31, 2016	$	10,095	$	129,888	$	139,983
Foreign currency translation adjustment		—		991		991

March 31, 2017	$	10,095	$	130,879	$	140,974

Intercompany Transactions. Centuri recognizes revenues generated from contracts with Southwest (see Note 3 – Segment Information). Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars):


	March 31, 2017		December 31, 2016
Centuri accounts receivable for services provided to Southwest	$	10,030	$	10,585

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

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


	March 31, 2017			December 31, 2016
Centuri property and equipment	$	462,094		$	451,114
Centuri accumulated provision for depreciation and amortization		(233,731	)		(228,374	)
Net cash surrender value of COLI policies		109,587			106,744
Other property		13,082			12,859

Total	$	351,032		$	342,343

Other Income (Deductions). The following table provides the composition of significant items included in Other income (deductions) in the condensed consolidated statements of income (thousands of dollars):


	Three Months Ended						Twelve Months Ended
	March 31						March 31
	2017			2016			2017			2016
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	2,800		$	900		$	9,300		$	(900	)
Interest income		564			367			2,045			1,537
Equity AFUDC		476			532			2,233			3,144
Miscellaneous income and (expense)		(229	)		(44	)		(3,446	)		(2,336	)

Southwest Gas Corporation - total other income (deductions)		3,611			1,755			10,132			1,445

Construction services segment:
Interest income		—			—			1			413
Foreign transaction gain (loss)		(1	)		(10	)		(13	)		(507	)
Miscellaneous income and (expense)		255			(24	)		1,493			977

Centuri total other income (deductions)		254			(34	)		1,481			883

Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	3,865		$	1,721		$	11,613		$	2,328

Included in the table above is the change in cash surrender values of company-owned life insurance (“COLI”) policies (including net death benefits recognized). 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. 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.

Recently Issued Accounting Standards Updates. In May 2014, the FASB issued the update “Revenue from Contracts with Customers (Topic 606).” The update replaces much of the current guidance regarding revenue recognition including most industry-specific guidance. In accordance with the update, an entity will be required to identify the contract with the customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In addition to the new revenue recognition requirements, entities will be required to disclose sufficient information to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. Entities may choose between two retrospective transition methods when applying the update. In July 2015, the FASB approved a one-year deferral of the effective date (annual periods beginning after December 15, 2017). In March, April, May, and December of 2016, the FASB issued updates to Topic 606 related to “Principal versus Agent Considerations (Reporting Revenue Gross versus Net)”, “Identifying Performance Obligations and Licensing”, “Narrow-Scope Improvements and Practical Expedients”, and certain “Technical Corrections and Improvements”. The amendments in the first two updates, respectively, provide guidance when another party, along with the entity, is involved in providing a good or service to a customer, and provide clarification with regard to identifying performance obligations and of the licensing implementation guidance in Topic 606. The third update includes improvements to the guidance on collectability, noncash consideration, and completed contracts at transition. In addition, a practical expedient is provided for contract modifications at transition and an accounting policy election related to the presentation of sales taxes and other similar taxes collected from customers. The fourth update affects narrow aspects of the guidance as issued to date. Management plans to adopt all of these updates at the required adoption date, which is for interim and annual reporting periods commencing January 2018.

Management has substantially completed the evaluation of the sources of revenue and is currently assessing the effect of the new guidance on its financial position, results of operations and cash flows. The final assessment is contingent, in part, upon the completion of reviews related to customers with negotiated and unique billing terms. Deliberations have been ongoing by the utility industry, notably in connection with efforts to produce an accounting guide intended to be developed by the American Institute of Certified Public Accountants (“AICPA”). In association with this undertaking, the AICPA formed a number of industry task forces, including a Power & Utilities (“P&U”) Task Force, on which Company personnel actively participate via formal membership. Industry representatives and organizations, the largest auditing firms, the AICPA’s Revenue Recognition Working Group and its Financial Reporting Executive Committee have undertaken, and continue to undertake, consideration of several items relevant to the utility industry. Where applicable or necessary, the FASB’s Transition Resource Group (“TRG”) is also participating. Through the P&U Task Force undertakings to date, general determinations have been made that contributions received in aid of construction (“CIAC”) efforts related to the industry’s pipe distribution and transmission systems are reimbursements of expenditures rather than revenue (consistent with current accounting practices). Furthermore, regarding the “collectibility” criterion in the update that must be met for revenue recognition, general determinations have been made that contracts for utility service (including service to lower income or lower credit quality customers) represent genuine and valid contracts for which revenue is able to be recognized when service is rendered (consistent with current accounting practices). These determinations by the P&U industry are based on the various measures our industry takes to help ensure collectibility (e.g., proof of creditworthiness, customer deposits, late fee assessment, disconnection, service re-establishment fees, collection processes, etc.), in addition to the regulatory mechanisms established under rate regulation to mitigate the impacts of individual customer nonpayment. A timeline for the resolution of all deliberations of P&U efforts has not been established. Southwest continues to actively work with its peers in the rate-regulated natural gas industry and with the public accounting profession to finalize the accounting treatment for several other issues that are not expected to be addressed by the P&U Task Force.

As of March 31, 2017, the construction services segment has substantially completed the evaluation of sources of revenue and continues to assess the effect of the new guidance on financial position, results of operations and cash flows. The principals of the new revenue recognition guidance are very similar to existing guidance for construction contractors. Similar to the P&U Task Force noted above, the AICPA formed the Engineering and Construction Contractors Task Force to assist the construction industry with implementing the new guidance. The accounting guide the AICPA intends to release is expected to provide implementation guidance related to several issues including 1) combining contracts and separating performance obligations; 2) estimating change orders, incentives, penalties, liquidated damages and other variable consideration items and 3) acceptable measures of progress when recognizing revenue over time.

Given the uncertainty with respect to the conclusions that might arise from the ongoing deliberations on issues associated with both the natural gas and construction services segments, the Company is currently unable to determine the effect the new guidance will have on its financial position, results of operations, cash flows, business processes, or the transition method it will utilize to adopt the new guidance. However, conclusions reached regarding CIAC and collectability criterion with regard to utility service are significant and are aligned with current practices and recognition.

In January 2016, the FASB issued the update “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” in order to improve the recognition and measurement of financial instruments. The update makes targeted improvements to existing U.S. GAAP by: 1) requiring equity investments to be measured at fair value with changes in fair value recognized in net income; 2) requiring the use of the exit price notion when measuring the fair value of financial instruments for disclosure purposes; 3) requiring separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements; 4) eliminating the requirement to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet; and 5) requiring a reporting entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in instrument-specific credit risk when the organization has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. All entities can early adopt the provision to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. Management is evaluating what impact, if any, this update might have on its consolidated financial statements and disclosures.

In February 2016, the FASB issued the update “Leases (Topic 842)”. Under the update, lessees will be required to recognize the following for all leases (with the exception of short-term leases) at the commencement date:

•

A lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and

•

A right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term.

Under the new guidance, lessor accounting is largely unchanged. Certain targeted improvements were made to align, where necessary, lessor accounting with the lessee accounting model and Topic 606, Revenue from Contracts with Customers. Though companies have historically been required to make disclosures regarding leases and of contractual obligations, leases (with terms longer than a year) will no longer exist off-balance sheet. Lessees (for capital and operating leases) and lessors (for sales-type, direct financing, and operating leases) must apply a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. The modified retrospective approach would not require any transition accounting for leases that expired before the earliest comparative period presented. Lessees and lessors may not apply a full retrospective transition approach. Early application is permitted. Management currently plans to adopt the update at the required adoption date, which is for interim and annual reporting periods commencing January 1, 2019. Existing leases have been documented by both segments and management is in the process of determining if special software will be necessary to implement the standard. In addition, management is evaluating the potential impacts of various natural gas industry-related issues in light of the leasing standard. Given the uncertainty with respect to the conclusions that might arise from these deliberations, management is currently unable to determine the effect the new guidance will have on its financial position, results of operations, cash flows, or business processes.

In June 2016, the FASB issued the update “Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments”. The update amends guidance on reporting credit losses for financial assets held at amortized cost basis and available for sale debt securities. For assets held at amortized cost basis, the update eliminates the “probable” threshold for initial recognition of credit losses in current U.S. GAAP and, instead, requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial asset to present the net amount expected to be collected. For available for sale debt securities, credit losses should be measured in a manner similar to current U.S. GAAP, however the update will require that credit losses be presented as an allowance rather than as a write-down. This update affects entities holding financial assets and net investment in leases that are not accounted for at fair value through net income. The update affects loans, debt securities, trade receivables, net investments in leases, off-balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope that have the contractual right to receive cash. The update is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. All entities may adopt the amendments in this update earlier as of fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Management is evaluating what impact, if any, this update might have on its consolidated financial statements and disclosures.

In August 2016, the FASB issued the update “Classification of Certain Cash Receipts and Cash Payments”. This update addresses the following specific cash flow issues: debt prepayment or debt extinguishment costs; settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance (“COLI”) policies; distributions received from equity method investees; beneficial interests in securitization transactions; and separately identifiable cash flows, including identification of the predominant nature in cases where cash receipts and payments have aspects of more than one class of cash flows. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. Management is evaluating the impacts this update might have on its consolidated cash flow statements and disclosures.

In October 2016, the FASB issued the update “Accounting for Income Taxes: Intra-Entity Asset Transfers of Assets Other than Inventory.” This update eliminates the current U.S. GAAP exception for all intra-entity sales of assets other than inventory. As a result, a reporting entity would recognize the tax expense from the sale of the asset in the seller’s tax jurisdiction when the transfer occurs, even though the pre-tax effects of that transaction are eliminated in consolidation. Any deferred tax asset that arises in the buyer’s jurisdiction would also be recognized at the time of the transfer. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted; however, the guidance can only be adopted in the first interim period of a fiscal year. No such election to adopt early was made by management. The modified retrospective approach will be required for transition to the new guidance, with a cumulative-effect adjustment recorded in retained earnings as of the beginning of the period of adoption. Management is evaluating the impacts this update might have on its consolidated financial statements.

In January 2017, the FASB issued the update “Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” The update eliminates Step 2 from the goodwill impairment test. The annual, or interim, goodwill impairment test is performed by comparing the fair value of a reporting unit with its carrying amount. An impairment charge should be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. In addition, income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit should be considered when measuring the goodwill impairment loss, if applicable. The update also eliminates the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The amendments should be applied on a prospective basis. The update is effective for fiscal and interim periods beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. Management has determined that this update would have had no impact on the consolidated financial statements for the periods presented if it had been effective during those periods.

In March 2017, the FASB issued the update “Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” The update applies to all employers that offer to their employees defined benefit pension plans, other postretirement benefit plans, or other types of benefits accounted for under Topic 715, Compensation – Retirement Benefits. The update requires that an employer report the service cost component in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations, if one is presented, and be appropriately described (or disclosed in the notes when one is not presented). The update also allows only the service cost component (and not the other components of periodic benefit costs) to be eligible for capitalization when applicable, making no exception for specialized industries, including rate-regulated industries. Southwest is a rate-regulated utility offering pension and postretirement benefits to retired employees. Rate-regulated entities providing utility and transmission services have historically capitalized a portion of periodic benefit costs (including non-service cost components) in utility infrastructure (for instance, when productive labor is also charged to capital work orders). The portion capitalized becomes a component of depreciation rate development by efforts of companies and their regulatory commissions. The industry is currently evaluating whether this update could cause a difference (not currently existing), between accounting reflected in general purpose financial statements versus financial statements and information utilized for regulatory reporting and ratemaking purposes. Deliberations center on whether companies will be able to implement the provisions of the update for all purposes, only for general purpose financial reporting purposes, or whether regulatory reporting and economics will give effect to other related changes necessary in general purpose financial statements. If the provisions of the update cannot be implemented for all purposes, substantial effort could be required to maintain separate records and to provide reasonable reconciliation means for users of both. The update is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted. Due to the industry deliberations noted above, management has not fully completed its evaluation at this time. As efforts continue, management will be evaluating the various impacts this update will have on its consolidated financial statements and disclosures.

Components of Net Periodic Benefit Cost

3 Months Ended

Mar. 31, 2017

Text Block [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.

Net periodic benefit costs included in the table below are components of an overhead loading process associated with the cost of labor. The overhead process ultimately results in allocation of net periodic benefit costs to the same accounts to which productive labor is charged. As a result, net periodic benefit 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.


	Qualified Retirement Plan
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	5,848		$	5,709		$	22,972		$	24,552
Interest cost		11,520			11,506			46,041			44,677
Expected return on plan assets		(13,799	)		(14,140	)		(56,217	)		(57,496	)
Amortization of net actuarial loss		6,001			6,317			24,950			30,875

Net periodic benefit cost	$	9,570		$	9,392		$	37,746		$	42,608


	SERP
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	78		$	82		$	327		$	322
Interest cost		471			465			1,865			1,737
Amortization of net actuarial loss		360			346			1,397			1,315

Net periodic benefit cost	$	909		$	893		$	3,589		$	3,374


	PBOP
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	367		$	374		$	1,492		$	1,604
Interest cost		808			796			3,192			3,046
Expected return on plan assets		(840	)		(788	)		(3,201	)		(3,386	)
Amortization of prior service costs		334			334			1,335			1,336
Amortization of net actuarial loss		—			104			313			362

Net periodic benefit cost	$	669		$	820		$	3,131		$	2,962

Segment Information

3 Months Ended

Mar. 31, 2017

Segment Reporting [Abstract]

Segment Information

Note 3 – Segment Information

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


	Natural Gas		Construction
	Operations		Services			Other			Total
Three months ended March 31, 2017
Revenues from external customers	$	462,602	$	170,839		$	—		$	633,441
Intersegment revenues		—		21,296			—			21,296

Total	$	462,602	$	192,135		$	—		$	654,737

Segment net income (loss)	$	76,938	$	(7,334	)	$	(296	)	$	69,308

Three months ended March 31, 2016
Revenues from external customers	$	525,100	$	183,961		$	—		$	709,061
Intersegment revenues		—		22,187			—			22,187

Total	$	525,100	$	206,148		$	—		$	731,248

Segment net income (loss)	$	77,583	$	(2,137	)	$	—		$	75,446


	Natural Gas		Construction
	Operations		Services			Other			Total
Twelve months ended March 31, 2017
Revenues from external customers	$	1,258,914	$	1,027,835		$	—		$	2,286,749
Intersegment revenues		—		97,230			—			97,230

Total	$	1,258,914	$	1,125,065		$	—		$	2,383,979

Segment net income (loss)	$	118,778	$	27,421		$	(296	)	$	145,903

Twelve months ended March 31, 2016
Revenues from external customers	$	1,426,624	$	927,742		$	—		$	2,354,366
Intersegment revenues		—		106,287			—			106,287

Total	$	1,426,624	$	1,034,029		$	—		$	2,460,653

Segment net income	$	110,287	$	31,493		$	—		$	141,780

- 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8971-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8595-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8380-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8984-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9031-108599

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9054-108599

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8538-108599

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 29
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8864-108599

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8924-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8906-108599

+ Details

Derivatives and Fair Value Measurements

3 Months Ended

Mar. 31, 2017

Fair Value Disclosures [Abstract]

Derivatives and Fair Value Measurements

Note 4 – Derivatives and Fair Value Measurements

Derivatives. In managing its natural gas supply portfolios, Southwest has historically entered into fixed- and variable-price contracts, which qualify as derivatives. Additionally, Southwest utilizes fixed-for-floating swap contracts (“Swaps”) to supplement its fixed-price contracts. The fixed-price contracts, firm commitments to purchase a fixed amount of gas in the future at a fixed price, qualify for the normal purchases and normal sales exception that is allowed for contracts that are probable of delivery in the normal course of business, and are exempt from fair value reporting. The variable-price contracts have no significant market value. The Swaps are recorded at fair value.

The fixed-price contracts and Swaps are utilized by Southwest under its volatility mitigation programs to effectively fix the price on a portion (up to 25% in the Arizona and California jurisdictions) of its natural gas supply portfolios. The maturities of the Swaps highly correlate to forecasted purchases of natural gas, during time frames ranging from April 2017 through March 2019. Under such contracts, Southwest pays the counterparty a fixed rate and receives from the counterparty a floating rate per MMBtu (“dekatherm”) of natural gas. Only the net differential is actually paid or received. The differential is calculated based on the notional amounts under the contracts, which are detailed in the table below (thousands of dekatherms):


	March 31, 2017		December 31, 2016
Contract notional amounts		8,799		10,543

Southwest does not utilize derivative financial instruments for speculative purposes, nor does it have trading operations.

The following table sets forth the gains and (losses) recognized on the Swaps (derivatives) for the three- and twelve-month periods ended March 31, 2017 and 2016 and their location in the Condensed Consolidated Statements of Income for both the Company and Southwest:

Gains (losses) recognized in income for derivatives not designated as hedging instruments:

(Thousands of dollars)


		Three Months Ended						Twelve Months Ended
	Location of Gain or (Loss)	March 31						March 31
Instrument	Recognized in Income on Derivative	2017			2016			2017			2016
Swaps	Net cost of gas sold	$	(5,137	)	$	(1,212	)	$	1,081		$	(6,696	)
Swaps	Net cost of gas sold		5,137	*		1,212	*		(1,081	)*		6,696	*

Total		$	—		$	—		$	—		$	—

*	Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.

No gains (losses) were recognized in net income or other comprehensive income during the periods presented for derivatives designated as cash flow hedging instruments. Previously, Southwest entered into two forward-starting interest rate swaps (“FSIRS”), both of which were designated cash flow hedges, to partially hedge the risk of interest rate variability during the period leading up to the planned issuance of debt. The first FSIRS terminated in December 2010. The second FSIRS terminated in March 2012. Losses on both FSIRS are being amortized over ten-year periods from Accumulated other comprehensive income (loss) into interest expense.

The following table sets forth the fair values of the Swaps and their location in the Condensed Consolidated Balance Sheets for both the Company and Southwest (thousands of dollars):

Fair values of derivatives not designated as hedging instruments:


March 31, 2017 Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total
Swaps	Prepaids and other current assets	$	142	$	(20	)	$	122
Swaps	Other current liabilities		167		(697	)		(530	)
Swaps	Other deferred credits		—		(736	)		(736	)

Total		$	309	$	(1,453	)	$	(1,144	)


December 31, 2016 Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total
Swaps	Deferred charges and other assets	$	899	$	(54	)	$	845
Swaps	Prepaids and other current assets		3,551		(19	)		3,532

Total		$	4,450	$	(73	)	$	4,377

The estimated fair values of the natural gas derivatives were determined using future natural gas index prices (as more fully described below). Master netting arrangements exist with each counterparty that provide for the net settlement (in the settlement month) of all contracts through a single payment. As applicable, management has elected to reflect the net amounts in its balance sheets. There was no outstanding collateral associated with the Swaps during either period shown in the above table.

Pursuant to regulatory deferral accounting treatment for rate-regulated entities, unrealized gains and losses in fair value of the Swaps are recorded as a regulatory asset and/or liability. When the Swaps mature, any prior positions held are reversed and the settled position is recorded as an increase or decrease of purchased gas under the related purchased gas adjustment (“PGA”) mechanism in determining its deferred PGA balances. Neither changes in fair value, nor settled amounts, of Swaps have a direct effect on earnings or other comprehensive income.

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


	Three Months Ended		Twelve Months Ended
(Thousands of dollars)	March 31, 2017		March 31, 2017
Paid to counterparties	$	1,301	$	2,560

Received from counterparties	$	1,685	$	2,411

The following table details the regulatory assets/(liabilities) offsetting the derivatives at fair value in the Condensed Consolidated Balance Sheets for both the Company and Southwest (thousands of dollars).


March 31, 2017 Instrument	Balance Sheet Location	Net Total
Swaps	Other current liabilities	$	(122	)
Swaps	Prepaids and other current assets		530
Swaps	Deferred charges and other assets		736

December 31, 2016 Instrument	Balance Sheet Location	Net Total
Swaps	Other deferred credits	$	(845	)
Swaps	Other current liabilities		(3,532	)

Fair Value Measurements. The estimated fair values of Southwest’s Swaps were determined at March 31, 2017 and December 31, 2016 using New York Mercantile Exchange (“NYMEX”) futures settlement prices for delivery of natural gas at Henry Hub adjusted by the price of NYMEX ClearPort basis Swaps, which reflect the difference between the price of natural gas at a given delivery basin and the Henry Hub pricing points. These Level 2 inputs (inputs, other than quoted prices, for similar assets or liabilities) are observable in the marketplace throughout the full term of the Swaps, but have been credit-risk adjusted with no significant impact to the overall fair value measurement.

The following table sets forth, by level within the three-level fair value hierarchy that ranks the inputs used to measure fair value by their reliability, the financial assets and liabilities that were accounted for at fair value by both the Company and Southwest:

Level 2 - Significant other observable inputs


(Thousands of dollars)	March 31, 2017			December 31, 2016
Assets at fair value:
Prepaids and other current assets - Swaps	$	122		$	3,532
Deferred charges and other assets - Swaps		—			845
Liabilities at fair value:
Other current liabilities - Swaps		(530	)		—
Other deferred credits - Swaps		(736	)		—

Net Assets (Liabilities)	$	(1,144	)	$	4,377

No financial assets or liabilities associated with the Swaps, which were accounted for at fair value, fell within Level 1 (quoted prices in active markets for identical financial assets) or Level 3 (significant unobservable inputs) of the fair value hierarchy.

With regard to the fair values of assets associated with pension and postretirement benefit plans, asset values were last updated as required as of December 2016. Refer to Note 10 – Pension and Other Post Retirement Benefits in the 2016 Annual Report to Shareholders on Form 10-K.

Common Stock	3 Months Ended
Common Stock	Mar. 31, 2017
Text Block [Abstract]
Common Stock	Note 5 – Common Stock In January 2017, the holding company reorganization was made effective and each outstanding share of Southwest Gas Corporation common stock was converted into a share of common stock in Southwest Gas Holdings, Inc., on a one-for-one basis. The ticker symbol of the stock, “SWX,” remained unchanged, and Southwest Gas Corporation became a wholly owned subsidiary of Southwest Gas Holdings, Inc. On March 29, 2017, the Company filed with the Securities Exchange Commission (“SEC”) an automatic shelf registration statement on Form S-3 (File No. 333-217018), which became effective upon filing, for the offer and sale of up to $150 million of common stock from time to time in at-the-market offerings under the prospectus included therein and in accordance with the Sales Agency Agreement, dated March 29, 2017, between the Company and BNY Mellon Capital Markets, LLC (the “Equity Shelf Program”). No shares of the Company’s common stock have been sold under that registration statement. During the three months ended March 31, 2017, the Company issued approximately 67,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Long-Term Debt

3 Months Ended

Mar. 31, 2017

Debt Disclosure [Abstract]

Long-Term Debt

Note 6 – Long-Term Debt

Carrying amounts of long-term debt and related estimated fair values as of March 31, 2017 and December 31, 2016 are disclosed in the following table. Southwest’s revolving credit facility (including commercial paper) and the variable-rate Industrial Development Revenue Bonds (“IDRBs”) approximate their carrying values, as they are repaid quickly (in the case of credit facility borrowings) and have interest rates that reset frequently. These are categorized as Level 1 due to Southwest’s ability to access similar debt arrangements at measurement dates with comparable terms, including variable rates. The fair values of Southwest’s debentures, senior notes, and fixed-rate IDRBs were determined utilizing a market-based valuation approach, where fair market values are determined based on evaluated pricing data, such as broker quotes and yields for similar securities adjusted for observable differences. Significant inputs used in the valuation generally include benchmark yield curves, credit ratings and issuer spreads. The external credit rating, coupon rate, and maturity of each security are considered in the valuation, as applicable. The market values of debentures and fixed-rate IDRBs are categorized as Level 2 (observable market inputs based on market prices of similar securities). The Centuri secured revolving credit and term loan facility and Centuri other debt obligations (not actively traded) are categorized as Level 3, based on significant unobservable inputs to their fair values. Since Centuri’s debt is not publicly traded, fair values for the secured revolving credit and term loan facility and other debt obligations were based on a conventional discounted cash flow methodology and utilized current market pricing yield curves, across Centuri’s debt maturity spectrum, of other industrial bonds with an assumed credit rating comparable to the Company’s.


	March 31, 2017					December 31, 2016
	Carrying			Market		Carrying			Market
	Amount			Value		Amount			Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 4.45%, due 2020	$	125,000		$	130,193	$	125,000		$	129,703
Notes, 6.1%, due 2041		125,000			150,255		125,000			149,734
Notes, 3.875%, due 2022		250,000			257,328		250,000			254,900
Notes, 4.875%, due 2043		250,000			264,968		250,000			266,793
Notes, 3.8%, due 2046		300,000			282,501		300,000			283,029
8% Series, due 2026		75,000			94,822		75,000			94,691
Medium-term notes, 7.59% series, due 2017		—			—		25,000			25,040
Medium-term notes, 7.78% series, due 2022		25,000			29,269		25,000			29,290
Medium-term notes, 7.92% series, due 2027		25,000			31,947		25,000			31,905
Medium-term notes, 6.76% series, due 2027		7,500			8,792		7,500			8,769
Unamortized discount and debt issuance costs		(9,788	)				(9,931	)

		1,172,712					1,197,569

Revolving credit facility and commercial paper		15,000			15,000		5,000			5,000

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		(2,397	)				(2,489	)

		197,603					197,511

Less: current maturities		—					(25,000	)

Long-term debt, less current maturities - Southwest Gas Corporation		1,385,315					1,375,080

Centuri:
Centuri term loan facility		105,358			105,944		106,700			106,819
Unamortized debt issuance costs		(485	)				(516	)

		104,873					106,184
Centuri secured revolving credit facility		51,054			51,144		41,185			41,292
Centuri other debt obligations		48,954			49,078		52,635			52,840
Less: current maturities		(26,064	)				(25,101	)

Long-term debt, less current maturities - Centuri		178,817					174,903

Consolidated Southwest Gas Holdings, Inc.:
Long-term debt		1,590,196					1,600,084
Less: current maturities		(26,064	)				(50,101	)

Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	1,564,132				$	1,549,983

In March 2017, Southwest amended its credit facility, increasing the borrowing capacity from $300 million to $400 million. Also, the facility was previously scheduled to expire in March 2021 and was extended to March 2022. Southwest continues to designate $150 million of capacity related to the facility as long-term debt and with the total capacity now available, has designated the remaining $250 million for working capital purposes. Interest rates for the credit facility are calculated at either the London Interbank Offered Rate (“LIBOR”) or an “alternate base rate,” plus in each case an applicable margin that is determined based on the Southwest’s senior unsecured debt rating. At March 31, 2017, the applicable margin is 1% for loans bearing interest with reference to LIBOR and 0% for loans bearing interest with reference to the alternative base rate. At March 31, 2017, $15 million was outstanding on the long-term and no borrowings were outstanding on the short-term portions of this credit facility.

Centuri has a $300 million secured revolving credit and term loan facility that is scheduled to expire in October 2019. At March 31, 2017, $156 million in borrowings were outstanding on the Centuri facility. Centuri assets securing the facility at March 31, 2017 totaled $412 million.

Short-Term Debt	3 Months Ended
Short-Term Debt	Mar. 31, 2017
Debt Disclosure [Abstract]
Short-Term Debt	Note 7 – Short-Term Debt In March 2017, Southwest Gas Holdings, Inc. entered into a credit facility with a borrowing capacity of $100 million that expires in March 2022. The Company intends to utilize this facility for short-term financing needs. Interest rates for this facility are calculated at either the LIBOR or the “alternate base rate,” plus in each case an applicable margin that is determined based on the Company’s senior unsecured debt rating. The applicable margin ranges from 0.75% to 1.5% for loans bearing interest with reference to LIBOR and from 0% to 0.5% for loans bearing interest with reference to the alternative base rate. The Company is also required to pay a commitment fee on the unfunded portion of the commitments based on its senior unsecured long-term debt rating. The commitment fee ranges from 0.075% to 0.2% per annum. At March 31, 2017, no borrowings were outstanding on this facility.

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income

3 Months Ended

Mar. 31, 2017

Equity [Abstract]

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income

Note 8 – Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income

The table below provides details of activity in equity and the redeemable noncontrolling interest for Southwest Gas Holdings, Inc. on a consolidated basis during the three months ended March 31, 2017.


	Southwest Gas Holdings, Inc. Equity
							Accumulated												Redeemable
					Additional		Other						Non-						Noncontrolling
	Common Stock				Paid-in		Comprehensive			Retained			controlling						Interest
(In thousands, except per share amounts)	Shares		Amount		Capital		Income (Loss)			Earnings			Interest			Total			(Temporary Equity)
DECEMBER 31, 2016		47,482	$	49,112	$	903,123	$	(48,008	)	$	759,263		$	(2,217	)	$	1,661,273		$	22,590
Common stock issuances		67		67		6,239											6,306
Net income (loss)											69,308			(45	)		69,263			(258	)
Redemption value adjustments											(1,288	)					(1,288	)		1,288
Foreign currency exchange translation adj.								213									213			7
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax								595									595
Amounts reclassified to net income, net of tax (FSIRS)								518									518
Centuri dividend to redeemable noncontrolling interest																				(102	)
Dividends declared
Common: $0.495 per share											(23,761	)					(23,761	)

MARCH 31, 2017		47,549	$	49,179	$	909,362	$	(46,682	)	$	803,522		$	(2,262	)	$	1,713,119		$	23,525

The table below provides details of activity in equity for Southwest Gas Corporation during the three months ended March 31, 2017. Effective in January 2017, Southwest became subsidiary of Southwest Gas Holdings, Inc., and only equity shares of the latter are publicly traded, under the ticker symbol “SWX.”


	Southwest Gas Corporation Equity
							Accumulated
					Additional		Other
	Common Stock				Paid-in		Comprehensive			Retained
(In thousands, except per share amounts)	Shares		Amount		Capital		Income (Loss)			Earnings			Total
DECEMBER 31, 2016		47,482	$	49,112	$	897,346	$	(45,639	)	$	767,061		$	1,667,880
Net income											76,938			76,938
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax								595						595
Amounts reclassified to net income, net of tax (FSIRS)								518						518
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations											(182,773	)		(182,773	)
Stock-based compensation (a)						5,906					(195	)		5,711
Dividends declared to Southwest Gas Holdings, Inc.											(18,530	)		(18,530	)

MARCH 31, 2017		47,482	$	49,112	$	903,252	$	(44,526	)	$	642,501		$	1,550,339

(a)	Stock-based compensation is based on stock awards of Southwest Gas Corporation to be issued in shares of Southwest Gas Holdings, Inc.

The table above gives effect to the holding company reorganization whereby Southwest and Centuri became subsidiaries of the Company. The historic investment in Centuri was distributed to the parent holding company. This presentation is only applicable to Southwest and not to the Company overall, as Centuri continues to be included in the continuing operations of the Company. Also in connection with the holding company creation, compensation plans of Southwest include programs that will be settled with equity shares issued by Southwest Gas Holdings, Inc. Management has determined that when no consideration is directly exchanged for these programs between Southwest and the Company, the accounting impact at Southwest for these programs is reflected both as compensation expense and as an equity contribution (of the parent) in Southwest.

The following information provides insight into amounts impacting the Company’s Other Comprehensive Income (Loss), both before and after-tax, within the Condensed Consolidated Statements of Comprehensive Income, which also impact Accumulated Other Comprehensive Income in the Condensed Consolidated Balance Sheets and the associated column in the equity table above, as well as the Redeemable Noncontrolling Interest. See Note 4 – Derivatives and Fair Value Measurements for additional information on the FSIRS.

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

(Thousands of dollars)


	Three Months Ended									Three Months Ended
	March 31, 2017									March 31, 2016
	Before-			Tax			Net-of-			Before-			Tax			Net-of-
	Tax			(Expense)			Tax			Tax			(Expense)			Tax
	Amount			or Benefit (1)			Amount			Amount			or Benefit (1)			Amount
Defined benefit pension plans:
Amortization of prior service cost	$	334		$	(127	)	$	207		$	334		$	(127	)	$	207
Amortization of net actuarial (gain)/loss		6,361			(2,417	)		3,944			6,767			(2,571	)		4,196
Regulatory adjustment		(5,735	)		2,179			(3,556	)		(6,123	)		2,327			(3,796	)

Pension plans other comprehensive income (loss)		960			(365	)		595			978			(371	)		607
FSIRS (designated hedging activities):
Amounts reclassifed into net income		836			(318	)		518			836			(317	)		519

FSIRS other comprehensive income		836			(318	)		518			836			(317	)		519

Total other comprehensive income (loss) - Southwest Gas Corporation		1,796			(683	)		1,113			1,814			(688	)		1,126

Foreign currency translation adjustments:
Translation adjustments		220			—			220			782			—			782

Foreign currency other comprehensive income (loss)		220			—			220			782			—			782

Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	2,016		$	(683	)	$	1,333		$	2,596		$	(688	)	$	1,908


	Twelve Months Ended									Twelve Months Ended
	March 31, 2017									March 31, 2016
	Before-			Tax			Net-of-			Before-			Tax			Net-of-
	Tax			(Expense)			Tax			Tax			(Expense)			Tax
	Amount			or Benefit (1)			Amount			Amount			or Benefit (1)			Amount
Defined benefit pension plans:
Net actuarial gain/(loss)	$	(22,770	)	$	8,652		$	(14,118	)	$	(30,519	)	$	11,597		$	(18,922	)
Amortization of prior service cost		1,335			(507	)		828			1,336			(507	)		829
Amortization of net actuarial (gain)/loss		26,660			(10,131	)		16,529			32,552			(12,370	)		20,182
Regulatory adjustment		(5,196	)		1,974			(3,222	)		(3,982	)		1,514			(2,468	)

Pension plans other comprehensive income (loss)		29			(12	)		17			(613	)		234			(379	)
FSIRS (designated hedging activities):
Amounts reclassifed into net income		3,345			(1,271	)		2,074			3,344			(1,271	)		2,073

FSIRS other comprehensive income (loss)		3,345			(1,271	)		2,074			3,344			(1,271	)		2,073

Total other comprehensive income (loss) - Southwest Gas Corporation		3,374			(1,283	)		2,091			2,731			(1,037	)		1,694

Foreign currency translation adjustments:
Translation adjustments		(401	)		—			(401	)		100			—			100

Foreign currency other comprehensive income (loss)		(401	)		—			(401	)		100			—			100

Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	2,973		$	(1,283	)	$	1,690		$	2,831		$	(1,037	)	$	1,794

(1)

Tax amounts are calculated using a 38% rate. The Company has elected to indefinitely reinvest the earnings of Centuri’s Canadian subsidiaries in Canada, thus preventing deferred taxes on such earnings. As a result of this assertion, the Company is not recognizing any tax effect or presenting a tax expense or benefit for the currency translation adjustment amount reported in Other Comprehensive Income, as repatriation of earnings is not anticipated.

Approximately $2.1 million of realized losses (net of tax) related to the FSIRS, reported in Accumulated other comprehensive income (“AOCI”) at March 31, 2017, will be reclassified into interest expense within the next 12 months as the related interest payments on long-term debt occur.

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

AOCI - Rollforward

(Thousands of dollars)


	Defined Benefit Plans									FSIRS									Foreign Currency Items
	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, 2016	$	(57,613	)	$	21,893		$	(35,720	)	$	(15,999	)	$	6,080		$	(9,919	)	$	(2,369	)	$	—	$	(2,369	)	$	(48,008	)

Translation adjustments		—			—			—			—			—			—			220			—		220			220

Other comprehensive income before reclassifications		—			—			—			—			—			—			220			—		220			220
FSIRS amounts reclassified from AOCI (1)		—			—			—			836			(318	)		518			—			—		—			518
Amortization of prior service cost (2)		334			(127	)		207			—			—			—			—			—		—			207
Amortization of net actuarial loss (2)		6,361			(2,417	)		3,944			—			—			—			—			—		—			3,944
Regulatory adjustment (3)		(5,735	)		2,179			(3,556	)		—			—			—			—			—		—			(3,556	)

Net current period other comprehensive income (loss)		960			(365	)		595			836			(318	)		518			220			—		220			1,333
Less: Translation adjustment attributable to redeemable noncontrolling interest		—			—			—			—			—			—			7			—		7			7

Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.		960			(365	)		595			836			(318	)		518			213			—		213			1,326

Ending Balance AOCI March 31, 2017	$	(56,653	)	$	21,528		$	(35,125	)	$	(15,163	)	$	5,762		$	(9,401	)	$	(2,156	)	$	—	$	(2,156	)	$	(46,682	)

(1)	The FSIRS reclassification amounts are included in the Net interest deductions line item 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 the Deferred charges and other assets line item on the Company’s Condensed Consolidated Balance Sheets).

(4)	Tax amounts are calculated using a 38% rate.

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

AOCI - Rollforward

(Thousands of dollars)


	Defined Benefit Plans									FSIRS
	Before-Tax			Tax (Expense) Benefit (8)			After-Tax			Before-Tax			Tax (Expense) Benefit (8)			After-Tax			AOCI
Beginning Balance AOCI December 31, 2016	$	(57,613	)	$	21,893		$	(35,720	)	$	(15,999	)	$	6,080		$	(9,919	)	$	(45,639	)

FSIRS amounts reclassified from AOCI (5)		—			—			—			836			(318	)		518			518
Amortization of prior service cost (6)		334			(127	)		207			—			—			—			207
Amortization of net actuarial loss (6)		6,361			(2,417	)		3,944			—			—			—			3,944
Regulatory adjustment (7)		(5,735	)		2,179			(3,556	)		—			—			—			(3,556	)

Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation		960			(365	)		595			836			(318	)		518			1,113

Ending Balance AOCI March 31, 2017	$	(56,653	)	$	21,528		$	(35,125	)	$	(15,163	)	$	5,762		$	(9,401	)	$	(44,526	)

(5)	The FSIRS reclassification amounts are included in the Net interest deductions line item 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 the Deferred charges and other assets line item on Southwest’s Condensed Consolidated Balance Sheets).

(8)	Tax amounts are calculated using a 38% 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:

Amounts Recognized in AOCI (Before Tax)

(Thousands of dollars)


	March 31, 2017			December 31, 2016
Net actuarial (loss) gain	$	(424,612	)	$	(430,973	)
Prior service cost		(5,369	)		(5,703	)
Less: amount recognized in regulatory assets		373,328			379,063

Recognized in AOCI	$	(56,653	)	$	(57,613	)

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 4.E)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(31))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 4.C)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6405834&loc=d3e23285-112656

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 16: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

+ Details

Construction Services Redeemable Noncontrolling Interest

3 Months Ended

Mar. 31, 2017

Noncontrolling Interest [Abstract]

Construction Services Redeemable Noncontrolling Interest

Note 9 – Construction Services Redeemable Noncontrolling Interest

In conjunction with the acquisition of the Canadian construction businesses in October 2014, the previous owners of the acquired companies currently hold a 3.4% equity interest in Centuri. The previous owners are able to exit their investment retained by requiring the purchase of a portion of their interest (a portion is already eligible for redemption). Incremental amounts will become eligible each year. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained is subject to the election beginning in July 2022. Due to the ability of the noncontrolling parties to redeem their interest for cash, their interest is presented on the Company’s Condensed Consolidated Balance Sheet at March 31, 2017 as a Redeemable noncontrolling interest, a category of mezzanine equity (temporary equity). The following depicts changes to the balance of the redeemable noncontrolling interest between the indicated periods.


	Redeemable Noncontrolling Interest
(Thousands of dollars):
Balance, December 31, 2016	$	22,590
Net income (loss) attributable to redeemable noncontrolling interest		(258	)
Foreign currency exchange translation adjustment		7
Centuri dividend to redeemable noncontrolling interest		(102	)
Adjustment to redemption value		1,288

Balance, March 31, 2017	$	23,525

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation

3 Months Ended

Mar. 31, 2017

Restructuring and Related Activities [Abstract]

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation

Note 10 – Reorganization Impacts – Discontinued Operations Solely Related to Southwest Gas Corporation

No substantive change has occurred with regard to the Company’s business segments on the whole, or in the primary businesses comprising those segments (Centuri operations continue to be part of continuing operations of the controlled group of companies), and financial information related to Centuri continues to be included in condensed consolidated financial statements of Southwest Gas Holdings, Inc.

However, as part of the holding company reorganization effective January 2017, Centuri is no longer a subsidiary of Southwest; whereas historically, Centuri had been a direct subsidiary of Southwest. To give effect to this change, the condensed consolidated financial statements related to Southwest Gas Corporation, which are separately included in this Form 10-Q, depict Centuri-related amounts as discontinued operations for periods prior to January 2017.

Due to the discontinued operations accounting reflection, the following disclosures provide additional information regarding the assets, liabilities, equity, revenues, and expenses of Centuri which are shown as discontinued operations on the condensed consolidated financial statements of Southwest Gas Corporation for periods prior to the beginning of 2017.

The following table presents the major categories of assets and liabilities within the amounts reported as discontinued operations – construction services in the Condensed Consolidated Balance Sheet of Southwest Gas Corporation:


(Thousands of dollars)	December 31, 2016
Assets:
Other property and investments	$	233,774
Cash and cash equivalents		9,042
Accounts receivable, net of allowances		173,300
Prepaids and other current assets		10,470
Goodwill		129,888
Other noncurrent assets		22,897

Discontinued operations - construction services - assets	$	579,371

Liabilities:
Current maturities of long-term debt	$	25,101
Accounts payable		46,440
Other current liabilities		74,518
Long-term debt, less current maturities		174,903
Deferred income taxes and other deferred credits		59,653

Discontinued operations - construction services - liabilities	$	380,615

The following table presents the components of the Discontinued operations – construction services non-owner equity amount shown in the Southwest Gas Corporation Condensed Consolidated Balance Sheet:


(Thousands of dollars)	December 31, 2016
Construction services equity	$	(4,390	)
Construction services noncontrolling interest		(2,217	)
Construction services redeemable noncontrolling interest		22,590

Discontinued operations - construction services non-owner equity	$	15,983

The following table presents the major income statement components of discontinued operations – construction services reported in the Condensed Consolidated Income Statements of Southwest Gas Corporation:


	Three			Twelve		Twelve
	Months Ended			Months Ended		Months Ended
(Thousands of dollars)	March 31, 2016			March 31, 2017		March 31, 2016
Construction revenues	$	206,148		$	932,930	$	1,034,029
Operating expenses:
Construction expenses		193,382			831,041		917,235
Depreciation and amortization		14,615			41,054		57,479

Operating income (loss)		(1,849	)		60,835		59,315
Other income (deductions)		(34	)		1,227		883
Net interest deductions		1,491			5,172		7,394

Income (loss) before income taxes		(3,374	)		56,890		52,804
Income tax expense (benefit)		(1,146	)		21,030		20,185

Net income (loss)		(2,228	)		35,860		32,619
Net income (loss) attributable to noncontrolling interests		(91	)		1,105		1,126

Discontinued operations - construction services - net income (loss)	$	(2,137	)	$	34,755	$	31,493

Nature of Operations and Basis of Presentation (Policies)

3 Months Ended

Mar. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Operations

Basis of Presentation

Prepaids and Other Current Assets

Cash and Cash Equivalents

Adoption of Accounting Standards Update

Goodwill


(In thousands of dollars)	Natural Gas Operations		Construction Services		Consolidated
December 31, 2016	$	10,095	$	129,888	$	139,983
Foreign currency translation adjustment		—		991		991

March 31, 2017	$	10,095	$	130,879	$	140,974

Intercompany Transactions


	March 31, 2017		December 31, 2016
Centuri accounts receivable for services provided to Southwest	$	10,030	$	10,585

Other Property and Investments

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


	March 31, 2017			December 31, 2016
Centuri property and equipment	$	462,094		$	451,114
Centuri accumulated provision for depreciation and amortization		(233,731	)		(228,374	)
Net cash surrender value of COLI policies		109,587			106,744
Other property		13,082			12,859

Total	$	351,032		$	342,343

Other Income (Deductions)


	Three Months Ended						Twelve Months Ended
	March 31						March 31
	2017			2016			2017			2016
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	2,800		$	900		$	9,300		$	(900	)
Interest income		564			367			2,045			1,537
Equity AFUDC		476			532			2,233			3,144
Miscellaneous income and (expense)		(229	)		(44	)		(3,446	)		(2,336	)

Southwest Gas Corporation - total other income (deductions)		3,611			1,755			10,132			1,445

Construction services segment:
Interest income		—			—			1			413
Foreign transaction gain (loss)		(1	)		(10	)		(13	)		(507	)
Miscellaneous income and (expense)		255			(24	)		1,493			977

Centuri total other income (deductions)		254			(34	)		1,481			883

Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	3,865		$	1,721		$	11,613		$	2,328

Recently Issued Accounting Standards Updates

•

A lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis; and

•

A right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term.

Nature of Operations and Basis of Presentation (Tables)

3 Months Ended

Mar. 31, 2017

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Goodwill


(In thousands of dollars)	Natural Gas Operations		Construction Services		Consolidated
December 31, 2016	$	10,095	$	129,888	$	139,983
Foreign currency translation adjustment		—		991		991

March 31, 2017	$	10,095	$	130,879	$	140,974

Accounts Receivable for Services

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


	March 31, 2017		December 31, 2016
Centuri accounts receivable for services provided to Southwest	$	10,030	$	10,585

Schedule of Other Property and Investments

Other property and investments on the Southwest Gas Holdings, Inc. Condensed Consolidated Balance Sheets includes (thousands of dollars):


	March 31, 2017			December 31, 2016
Centuri property and equipment	$	462,094		$	451,114
Centuri accumulated provision for depreciation and amortization		(233,731	)		(228,374	)
Net cash surrender value of COLI policies		109,587			106,744
Other property		13,082			12,859

Total	$	351,032		$	342,343

Other Income (Deductions)

The following table provides the composition of significant items included in Other income (deductions) in the condensed consolidated statements of income (thousands of dollars):


	Three Months Ended						Twelve Months Ended
	March 31						March 31
	2017			2016			2017			2016
Southwest Gas Corporation - natural gas operations segment:
Change in COLI policies	$	2,800		$	900		$	9,300		$	(900	)
Interest income		564			367			2,045			1,537
Equity AFUDC		476			532			2,233			3,144
Miscellaneous income and (expense)		(229	)		(44	)		(3,446	)		(2,336	)

Southwest Gas Corporation - total other income (deductions)		3,611			1,755			10,132			1,445

Construction services segment:
Interest income		—			—			1			413
Foreign transaction gain (loss)		(1	)		(10	)		(13	)		(507	)
Miscellaneous income and (expense)		255			(24	)		1,493			977

Centuri total other income (deductions)		254			(34	)		1,481			883

Consolidated Southwest Gas Holdings, Inc. - total other income (deductions)	$	3,865		$	1,721		$	11,613		$	2,328

Components of Net Periodic Benefit Cost (Tables)

3 Months Ended

Mar. 31, 2017

Text Block [Abstract]

Schedule of Net Periodic Benefit Costs


	Qualified Retirement Plan
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	5,848		$	5,709		$	22,972		$	24,552
Interest cost		11,520			11,506			46,041			44,677
Expected return on plan assets		(13,799	)		(14,140	)		(56,217	)		(57,496	)
Amortization of net actuarial loss		6,001			6,317			24,950			30,875

Net periodic benefit cost	$	9,570		$	9,392		$	37,746		$	42,608


	SERP
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	78		$	82		$	327		$	322
Interest cost		471			465			1,865			1,737
Amortization of net actuarial loss		360			346			1,397			1,315

Net periodic benefit cost	$	909		$	893		$	3,589		$	3,374


	PBOP
	Period Ended March 31,
	Three Months						Twelve Months
	2017			2016			2017			2016
(Thousands of dollars)
Service cost	$	367		$	374		$	1,492		$	1,604
Interest cost		808			796			3,192			3,046
Expected return on plan assets		(840	)		(788	)		(3,201	)		(3,386	)
Amortization of prior service costs		334			334			1,335			1,336
Amortization of net actuarial loss		—			104			313			362

Net periodic benefit cost	$	669		$	820		$	3,131		$	2,962

Segment Information (Tables)

3 Months Ended

Mar. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Reporting Information

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


	Natural Gas		Construction
	Operations		Services			Other			Total
Three months ended March 31, 2017
Revenues from external customers	$	462,602	$	170,839		$	—		$	633,441
Intersegment revenues		—		21,296			—			21,296

Total	$	462,602	$	192,135		$	—		$	654,737

Segment net income (loss)	$	76,938	$	(7,334	)	$	(296	)	$	69,308

Three months ended March 31, 2016
Revenues from external customers	$	525,100	$	183,961		$	—		$	709,061
Intersegment revenues		—		22,187			—			22,187

Total	$	525,100	$	206,148		$	—		$	731,248

Segment net income (loss)	$	77,583	$	(2,137	)	$	—		$	75,446


	Natural Gas		Construction
	Operations		Services			Other			Total
Twelve months ended March 31, 2017
Revenues from external customers	$	1,258,914	$	1,027,835		$	—		$	2,286,749
Intersegment revenues		—		97,230			—			97,230

Total	$	1,258,914	$	1,125,065		$	—		$	2,383,979

Segment net income (loss)	$	118,778	$	27,421		$	(296	)	$	145,903

Twelve months ended March 31, 2016
Revenues from external customers	$	1,426,624	$	927,742		$	—		$	2,354,366
Intersegment revenues		—		106,287			—			106,287

Total	$	1,426,624	$	1,034,029		$	—		$	2,460,653

Segment net income	$	110,287	$	31,493		$	—		$	141,780

Derivatives and Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2017

Fair Value Disclosures [Abstract]

Notional Amounts under Swaps Contracts

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


	March 31, 2017		December 31, 2016
Contract notional amounts		8,799		10,543

Amount of Gain or Losses Recognized in Income on Derivatives

Gains (losses) recognized in income for derivatives not designated as hedging instruments:

(Thousands of dollars)


		Three Months Ended						Twelve Months Ended
	Location of Gain or (Loss)	March 31						March 31
Instrument	Recognized in Income on Derivative	2017			2016			2017			2016
Swaps	Net cost of gas sold	$	(5,137	)	$	(1,212	)	$	1,081		$	(6,696	)
Swaps	Net cost of gas sold		5,137	*		1,212	*		(1,081	)*		6,696	*

Total		$	—		$	—		$	—		$	—

*	Represents the impact of regulatory deferral accounting treatment under U.S. GAAP for rate-regulated entities.

Fair Values of Swaps in Consolidated Balance Sheets

The following table sets forth the fair values of the Swaps and their location in the Condensed Consolidated Balance Sheets for both the Company and Southwest (thousands of dollars):

Fair values of derivatives not designated as hedging instruments:


March 31, 2017 Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total
Swaps	Prepaids and other current assets	$	142	$	(20	)	$	122
Swaps	Other current liabilities		167		(697	)		(530	)
Swaps	Other deferred credits		—		(736	)		(736	)

Total		$	309	$	(1,453	)	$	(1,144	)


December 31, 2016 Instrument	Balance Sheet Location	Asset Derivatives		Liability Derivatives			Net Total
Swaps	Deferred charges and other assets	$	899	$	(54	)	$	845
Swaps	Prepaids and other current assets		3,551		(19	)		3,532

Total		$	4,450	$	(73	)	$	4,377

Paid to and Received from Counterparties for Settlements of Matured Swaps

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


	Three Months Ended		Twelve Months Ended
(Thousands of dollars)	March 31, 2017		March 31, 2017
Paid to counterparties	$	1,301	$	2,560

Received from counterparties	$	1,685	$	2,411

Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets


March 31, 2017 Instrument	Balance Sheet Location	Net Total
Swaps	Other current liabilities	$	(122	)
Swaps	Prepaids and other current assets		530
Swaps	Deferred charges and other assets		736

December 31, 2016 Instrument	Balance Sheet Location	Net Total
Swaps	Other deferred credits	$	(845	)
Swaps	Other current liabilities		(3,532	)

Significant Other Observable Inputs

Level 2 - Significant other observable inputs


(Thousands of dollars)	March 31, 2017			December 31, 2016
Assets at fair value:
Prepaids and other current assets - Swaps	$	122		$	3,532
Deferred charges and other assets - Swaps		—			845
Liabilities at fair value:
Other current liabilities - Swaps		(530	)		—
Other deferred credits - Swaps		(736	)		—

Net Assets (Liabilities)	$	(1,144	)	$	4,377

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Long-Term Debt (Tables)

3 Months Ended

Mar. 31, 2017

Debt Disclosure [Abstract]

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

Since Centuri’s debt is not publicly traded, fair values for the secured revolving credit and term loan facility and other debt obligations were based on a conventional discounted cash flow methodology and utilized current market pricing yield curves, across Centuri’s debt maturity spectrum, of other industrial bonds with an assumed credit rating comparable to the Company’s.


	March 31, 2017					December 31, 2016
	Carrying			Market		Carrying			Market
	Amount			Value		Amount			Value
(Thousands of dollars)
Southwest Gas Corporation:
Debentures:
Notes, 4.45%, due 2020	$	125,000		$	130,193	$	125,000		$	129,703
Notes, 6.1%, due 2041		125,000			150,255		125,000			149,734
Notes, 3.875%, due 2022		250,000			257,328		250,000			254,900
Notes, 4.875%, due 2043		250,000			264,968		250,000			266,793
Notes, 3.8%, due 2046		300,000			282,501		300,000			283,029
8% Series, due 2026		75,000			94,822		75,000			94,691
Medium-term notes, 7.59% series, due 2017		—			—		25,000			25,040
Medium-term notes, 7.78% series, due 2022		25,000			29,269		25,000			29,290
Medium-term notes, 7.92% series, due 2027		25,000			31,947		25,000			31,905
Medium-term notes, 6.76% series, due 2027		7,500			8,792		7,500			8,769
Unamortized discount and debt issuance costs		(9,788	)				(9,931	)

		1,172,712					1,197,569

Revolving credit facility and commercial paper		15,000			15,000		5,000			5,000

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		(2,397	)				(2,489	)

		197,603					197,511

Less: current maturities		—					(25,000	)

Long-term debt, less current maturities - Southwest Gas Corporation		1,385,315					1,375,080

Centuri:
Centuri term loan facility		105,358			105,944		106,700			106,819
Unamortized debt issuance costs		(485	)				(516	)

		104,873					106,184
Centuri secured revolving credit facility		51,054			51,144		41,185			41,292
Centuri other debt obligations		48,954			49,078		52,635			52,840
Less: current maturities		(26,064	)				(25,101	)

Long-term debt, less current maturities - Centuri		178,817					174,903

Consolidated Southwest Gas Holdings, Inc.:
Long-term debt		1,590,196					1,600,084
Less: current maturities		(26,064	)				(50,101	)

Long-term debt, less current maturities - Southwest Gas Holdings, Inc.	$	1,564,132				$	1,549,983

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644

+ Details

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income (Tables)

3 Months Ended

Mar. 31, 2017

Detailed Activities of Equity and Redeemable Noncontrolling Interest


	Southwest Gas Holdings, Inc. Equity
							Accumulated												Redeemable
					Additional		Other						Non-						Noncontrolling
	Common Stock				Paid-in		Comprehensive			Retained			controlling						Interest
(In thousands, except per share amounts)	Shares		Amount		Capital		Income (Loss)			Earnings			Interest			Total			(Temporary Equity)
DECEMBER 31, 2016		47,482	$	49,112	$	903,123	$	(48,008	)	$	759,263		$	(2,217	)	$	1,661,273		$	22,590
Common stock issuances		67		67		6,239											6,306
Net income (loss)											69,308			(45	)		69,263			(258	)
Redemption value adjustments											(1,288	)					(1,288	)		1,288
Foreign currency exchange translation adj.								213									213			7
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax								595									595
Amounts reclassified to net income, net of tax (FSIRS)								518									518
Centuri dividend to redeemable noncontrolling interest																				(102	)
Dividends declared
Common: $0.495 per share											(23,761	)					(23,761	)

MARCH 31, 2017		47,549	$	49,179	$	909,362	$	(46,682	)	$	803,522		$	(2,262	)	$	1,713,119		$	23,525

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

(Thousands of dollars)


	Three Months Ended									Three Months Ended
	March 31, 2017									March 31, 2016
	Before-			Tax			Net-of-			Before-			Tax			Net-of-
	Tax			(Expense)			Tax			Tax			(Expense)			Tax
	Amount			or Benefit (1)			Amount			Amount			or Benefit (1)			Amount
Defined benefit pension plans:
Amortization of prior service cost	$	334		$	(127	)	$	207		$	334		$	(127	)	$	207
Amortization of net actuarial (gain)/loss		6,361			(2,417	)		3,944			6,767			(2,571	)		4,196
Regulatory adjustment		(5,735	)		2,179			(3,556	)		(6,123	)		2,327			(3,796	)

Pension plans other comprehensive income (loss)		960			(365	)		595			978			(371	)		607
FSIRS (designated hedging activities):
Amounts reclassifed into net income		836			(318	)		518			836			(317	)		519

FSIRS other comprehensive income		836			(318	)		518			836			(317	)		519

Total other comprehensive income (loss) - Southwest Gas Corporation		1,796			(683	)		1,113			1,814			(688	)		1,126

Foreign currency translation adjustments:
Translation adjustments		220			—			220			782			—			782

Foreign currency other comprehensive income (loss)		220			—			220			782			—			782

Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	2,016		$	(683	)	$	1,333		$	2,596		$	(688	)	$	1,908


	Twelve Months Ended									Twelve Months Ended
	March 31, 2017									March 31, 2016
	Before-			Tax			Net-of-			Before-			Tax			Net-of-
	Tax			(Expense)			Tax			Tax			(Expense)			Tax
	Amount			or Benefit (1)			Amount			Amount			or Benefit (1)			Amount
Defined benefit pension plans:
Net actuarial gain/(loss)	$	(22,770	)	$	8,652		$	(14,118	)	$	(30,519	)	$	11,597		$	(18,922	)
Amortization of prior service cost		1,335			(507	)		828			1,336			(507	)		829
Amortization of net actuarial (gain)/loss		26,660			(10,131	)		16,529			32,552			(12,370	)		20,182
Regulatory adjustment		(5,196	)		1,974			(3,222	)		(3,982	)		1,514			(2,468	)

Pension plans other comprehensive income (loss)		29			(12	)		17			(613	)		234			(379	)
FSIRS (designated hedging activities):
Amounts reclassifed into net income		3,345			(1,271	)		2,074			3,344			(1,271	)		2,073

FSIRS other comprehensive income (loss)		3,345			(1,271	)		2,074			3,344			(1,271	)		2,073

Total other comprehensive income (loss) - Southwest Gas Corporation		3,374			(1,283	)		2,091			2,731			(1,037	)		1,694

Foreign currency translation adjustments:
Translation adjustments		(401	)		—			(401	)		100			—			100

Foreign currency other comprehensive income (loss)		(401	)		—			(401	)		100			—			100

Total other comprehensive income (loss) - Southwest Gas Holdings, Inc.	$	2,973		$	(1,283	)	$	1,690		$	2,831		$	(1,037	)	$	1,794

(1)

Rollforward of Accumulated Other Comprehensive Income

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

AOCI - Rollforward

(Thousands of dollars)


	Defined Benefit Plans									FSIRS									Foreign Currency Items
	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, 2016	$	(57,613	)	$	21,893		$	(35,720	)	$	(15,999	)	$	6,080		$	(9,919	)	$	(2,369	)	$	—	$	(2,369	)	$	(48,008	)

Translation adjustments		—			—			—			—			—			—			220			—		220			220

Other comprehensive income before reclassifications		—			—			—			—			—			—			220			—		220			220
FSIRS amounts reclassified from AOCI (1)		—			—			—			836			(318	)		518			—			—		—			518
Amortization of prior service cost (2)		334			(127	)		207			—			—			—			—			—		—			207
Amortization of net actuarial loss (2)		6,361			(2,417	)		3,944			—			—			—			—			—		—			3,944
Regulatory adjustment (3)		(5,735	)		2,179			(3,556	)		—			—			—			—			—		—			(3,556	)

Net current period other comprehensive income (loss)		960			(365	)		595			836			(318	)		518			220			—		220			1,333
Less: Translation adjustment attributable to redeemable noncontrolling interest		—			—			—			—			—			—			7			—		7			7

Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc.		960			(365	)		595			836			(318	)		518			213			—		213			1,326

Ending Balance AOCI March 31, 2017	$	(56,653	)	$	21,528		$	(35,125	)	$	(15,163	)	$	5,762		$	(9,401	)	$	(2,156	)	$	—	$	(2,156	)	$	(46,682	)

(1)	The FSIRS reclassification amounts are included in the Net interest deductions line item 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 the Deferred charges and other assets line item on the Company’s Condensed Consolidated Balance Sheets).

(4)	Tax amounts are calculated using a 38% rate.

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:

Amounts Recognized in AOCI (Before Tax)

(Thousands of dollars)


	March 31, 2017			December 31, 2016
Net actuarial (loss) gain	$	(424,612	)	$	(430,973	)
Prior service cost		(5,369	)		(5,703	)
Less: amount recognized in regulatory assets		373,328			379,063

Recognized in AOCI	$	(56,653	)	$	(57,613	)

Southwest Gas Corporation [Member]

Detailed Activities of Equity and Redeemable Noncontrolling Interest


	Southwest Gas Corporation Equity
							Accumulated
					Additional		Other
	Common Stock				Paid-in		Comprehensive			Retained
(In thousands, except per share amounts)	Shares		Amount		Capital		Income (Loss)			Earnings			Total
DECEMBER 31, 2016		47,482	$	49,112	$	897,346	$	(45,639	)	$	767,061		$	1,667,880
Net income											76,938			76,938
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax								595						595
Amounts reclassified to net income, net of tax (FSIRS)								518						518
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations											(182,773	)		(182,773	)
Stock-based compensation (a)						5,906					(195	)		5,711
Dividends declared to Southwest Gas Holdings, Inc.											(18,530	)		(18,530	)

MARCH 31, 2017		47,482	$	49,112	$	903,252	$	(44,526	)	$	642,501		$	1,550,339

Rollforward of Accumulated Other Comprehensive Income

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

AOCI - Rollforward

(Thousands of dollars)


	Defined Benefit Plans									FSIRS
	Before-Tax			Tax (Expense) Benefit (8)			After-Tax			Before-Tax			Tax (Expense) Benefit (8)			After-Tax			AOCI
Beginning Balance AOCI December 31, 2016	$	(57,613	)	$	21,893		$	(35,720	)	$	(15,999	)	$	6,080		$	(9,919	)	$	(45,639	)

FSIRS amounts reclassified from AOCI (5)		—			—			—			836			(318	)		518			518
Amortization of prior service cost (6)		334			(127	)		207			—			—			—			207
Amortization of net actuarial loss (6)		6,361			(2,417	)		3,944			—			—			—			3,944
Regulatory adjustment (7)		(5,735	)		2,179			(3,556	)		—			—			—			(3,556	)

Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation		960			(365	)		595			836			(318	)		518			1,113

Ending Balance AOCI March 31, 2017	$	(56,653	)	$	21,528		$	(35,125	)	$	(15,163	)	$	5,762		$	(9,401	)	$	(44,526	)

(5)	The FSIRS reclassification amounts are included in the Net interest deductions line item 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 the Deferred charges and other assets line item on Southwest’s Condensed Consolidated Balance Sheets).

(8)	Tax amounts are calculated using a 38% rate.

Construction Services Redeemable Noncontrolling Interest (Tables)

3 Months Ended

Mar. 31, 2017

Noncontrolling Interest [Abstract]

Summary of Redeemable Noncontrolling Interest

The following depicts changes to the balance of the redeemable noncontrolling interest between the indicated periods.


	Redeemable Noncontrolling Interest
(Thousands of dollars):
Balance, December 31, 2016	$	22,590
Net income (loss) attributable to redeemable noncontrolling interest		(258	)
Foreign currency exchange translation adjustment		7
Centuri dividend to redeemable noncontrolling interest		(102	)
Adjustment to redemption value		1,288

Balance, March 31, 2017	$	23,525

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation (Tables)

3 Months Ended

Mar. 31, 2017

Restructuring and Related Activities [Abstract]

Summary of Discontinued Operations - Construction Services in Condensed Consolidated Balance Sheet and Condensed Consolidated Income Statements


(Thousands of dollars)	December 31, 2016
Assets:
Other property and investments	$	233,774
Cash and cash equivalents		9,042
Accounts receivable, net of allowances		173,300
Prepaids and other current assets		10,470
Goodwill		129,888
Other noncurrent assets		22,897

Discontinued operations - construction services - assets	$	579,371

Liabilities:
Current maturities of long-term debt	$	25,101
Accounts payable		46,440
Other current liabilities		74,518
Long-term debt, less current maturities		174,903
Deferred income taxes and other deferred credits		59,653

Discontinued operations - construction services - liabilities	$	380,615


(Thousands of dollars)	December 31, 2016
Construction services equity	$	(4,390	)
Construction services noncontrolling interest		(2,217	)
Construction services redeemable noncontrolling interest		22,590

Discontinued operations - construction services non-owner equity	$	15,983


	Three			Twelve		Twelve
	Months Ended			Months Ended		Months Ended
(Thousands of dollars)	March 31, 2016			March 31, 2017		March 31, 2016
Construction revenues	$	206,148		$	932,930	$	1,034,029
Operating expenses:
Construction expenses		193,382			831,041		917,235
Depreciation and amortization		14,615			41,054		57,479

Operating income (loss)		(1,849	)		60,835		59,315
Other income (deductions)		(34	)		1,227		883
Net interest deductions		1,491			5,172		7,394

Income (loss) before income taxes		(3,374	)		56,890		52,804
Income tax expense (benefit)		(1,146	)		21,030		20,185

Net income (loss)		(2,228	)		35,860		32,619
Net income (loss) attributable to noncontrolling interests		(91	)		1,105		1,126

Discontinued operations - construction services - net income (loss)	$	(2,137	)	$	34,755	$	31,493

- Definition

Tabular disclosure of information related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 4B
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721665-107760

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1474-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721683-107760

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=64862545&loc=SL51724579-110230

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5C
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721675-107760

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 4A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721663-107760

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2941-110230

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721673-107760

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721659-107760

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5A
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721671-107760

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5D
-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721677-107760

+ Details

Nature of Operations and Basis of Presentation - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Non-cash construction advances - non-cash investing item	$ 477,000	$ 900,000
Accrued taxes	20,397,000	38,196,000	$ 10,660,000	$ (18,118,000)
Goodwill impairment charges	$ 0
Centuri Construction Group Inc [Member]
Significant Accounting Policies [Line Items]
Ownership percentage in subsidiary	96.60%
Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes	$ 25,176,000	36,049,000	10,637,000	(18,047,000)
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		38,196,000		(18,118,000)
Accounting Standards Update 2016-09 [Member] \| Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		36,049,000		(18,047,000)
Accounting Standards Update 2016-09 [Member] \| Scenario, Previously Reported [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		36,300,000		(21,900,000)
Accounting Standards Update 2016-09 [Member] \| Scenario, Previously Reported [Member] \| Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		$ 34,200,000		$ (21,800,000)
Pooled Funds and Mutual Funds [Member] \| Level 2 - Significant Other Observable Inputs [Member]
Significant Accounting Policies [Line Items]
Money market fund investments	14,100,000		14,100,000		$ 5,300,000
Gas Pipe Materials and Supplies [Member]
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies	$ 35,000,000		$ 35,000,000		$ 30,000,000

Nature of Operations and Basis of Presentation - Schedule of Goodwill (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill, Beginning balance	$ 139,983
Foreign currency translation adjustment	991
Goodwill, Ending balance	140,974
Natural Gas Operations [Member]
Goodwill [Line Items]
Goodwill, Beginning balance	10,095
Foreign currency translation adjustment	0
Goodwill, Ending balance	10,095
Construction Services [Member]
Goodwill [Line Items]
Goodwill, Beginning balance	129,888
Foreign currency translation adjustment	991
Goodwill, Ending balance	$ 130,879

Nature of Operations and Basis of Presentation - Accounts Receivable for Services (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Centuri Construction Group Inc [Member]
Segment Reporting Information [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 10,030	$ 10,585

Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Net cash surrender value of COLI policies	$ 109,587	$ 106,744
Other property	13,082	12,859
Total	351,032	342,343
Centuri Construction Group Inc [Member]
Investment [Line Items]
Centuri property and equipment	462,094	451,114
Centuri accumulated provision for depreciation and amortization	$ (233,731)	$ (228,374)

Nature of Operations and Basis of Presentation - Other Income (Deductions) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Other income (deductions)
Total other income (deductions)	$ 3,865	$ 1,721	$ 11,613	$ 2,328
Southwest Gas Corporation [Member]
Other income (deductions)
Change in COLI policies	2,800	900	9,300	(900)
Interest income	564	367	2,045	1,537
Equity AFUDC	476	532	2,233	3,144
Miscellaneous income and (expense)	(229)	(44)	(3,446)	(2,336)
Total other income (deductions)	3,611	1,755	10,132	1,445
Centuri Construction Group Inc [Member]
Other income (deductions)
Interest income			1	413
Foreign transaction gain (loss)	(1)	(10)	(13)	(507)
Miscellaneous income and (expense)	255	(24)	1,493	977
Total other income (deductions)	$ 254	$ (34)	$ 1,481	$ 883

Components of Net Periodic Benefit Cost - Schedule of Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Qualified Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,848	$ 5,709	$ 22,972	$ 24,552
Interest cost	11,520	11,506	46,041	44,677
Expected return on plan assets	(13,799)	(14,140)	(56,217)	(57,496)
Amortization of net actuarial loss	6,001	6,317	24,950	30,875
Net periodic benefit cost	9,570	9,392	37,746	42,608
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	78	82	327	322
Interest cost	471	465	1,865	1,737
Amortization of net actuarial loss	360	346	1,397	1,315
Net periodic benefit cost	909	893	3,589	3,374
PBOP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	367	374	1,492	1,604
Interest cost	808	796	3,192	3,046
Expected return on plan assets	(840)	(788)	(3,201)	(3,386)
Amortization of prior service costs	334	334	1,335	1,336
Amortization of net actuarial loss		104	313	362
Net periodic benefit cost	$ 669	$ 820	$ 3,131	$ 2,962

Segment Information - Additional Information (Detail)	3 Months Ended
Segment Information - Additional Information (Detail)	Mar. 31, 2017 Segment
Segment Reporting Information [Line Items]
Number of segments	2
Southwest Gas Corporation [Member]
Segment Reporting Information [Line Items]
Number of segments	1

Segment Information - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 633,441	$ 709,061	$ 2,286,749	$ 2,354,366
Segment net income (loss)	69,308	75,446	145,903	141,780
Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	21,296	22,187	97,230	106,287
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	654,737	731,248	2,383,979	2,460,653
Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Revenues	462,602	525,100	1,258,914	1,426,624
Segment net income (loss)	76,938	77,583	118,778	110,287
Natural Gas Operations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	462,602	525,100	1,258,914	1,426,624
Construction Services [Member]
Segment Reporting Information [Line Items]
Revenues	170,839	183,961	1,027,835	927,742
Segment net income (loss)	(7,334)	(2,137)	27,421	31,493
Construction Services [Member] \| Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	21,296	22,187	97,230	106,287
Construction Services [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	192,135	$ 206,148	1,125,065	$ 1,034,029
Other [Member]
Segment Reporting Information [Line Items]
Segment net income (loss)	$ (296)		$ (296)

Derivatives and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Derivative [Line Items]
Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges	$ 518,000	$ 519,000	$ 2,074,000	$ 2,073,000
Derivative instrument loss at settlement amortization period	10 years
Cash Flow Hedging [Member]
Derivative [Line Items]
Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges	$ 0
Minimum [Member]
Derivative [Line Items]
Maturities of natural gas swaps	Apr. 30, 2017
Maximum [Member]
Derivative [Line Items]
Maturities of natural gas swaps	Mar. 31, 2019
Arizona [Member]
Derivative [Line Items]
Natural gas portfolios, maximum % rate	25.00%
California [Member]
Derivative [Line Items]
Natural gas portfolios, maximum % rate	25.00%

Derivatives and Fair Value Measurements - Notional Amounts under Swaps Contracts (Detail) - MMBTU	Mar. 31, 2017	Dec. 31, 2016
Offsetting [Abstract]
Contract notional amounts	8,799,000	10,543,000

Derivatives and Fair Value Measurements - Amount of Gain or Losses Recognized in Income on Derivatives (Detail) - Cash Flow Hedging [Member] - Net Cost of Gas Sold [Member] - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ (5,137)	$ (1,212)	$ 1,081	$ (6,696)
Regulatory Deferral Accounting Treatment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ 5,137	$ 1,212	$ (1,081)	$ 6,696

Derivatives and Fair Value Measurements - Fair Values of Swaps in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 309	$ 4,450
Liability derivatives not designated as hedging instruments	(1,453)	(73)
Net total not designated as hedging instruments	(1,144)	4,377
Swaps [Member] \| Deferred Charges and Other Assets [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments		899
Liability derivatives not designated as hedging instruments		(54)
Net total not designated as hedging instruments		845
Swaps [Member] \| Prepaids and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	142	3,551
Liability derivatives not designated as hedging instruments	(20)	(19)
Net total not designated as hedging instruments	122	$ 3,532
Swaps [Member] \| Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	167
Liability derivatives not designated as hedging instruments	(697)
Net total not designated as hedging instruments	(530)
Swaps [Member] \| Other Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Liability derivatives not designated as hedging instruments	(736)
Net total not designated as hedging instruments	$ (736)

Derivatives and Fair Value Measurements - Paid to and Received from Counterparties for Settlements of Matured Swaps (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Paid to counterparties	$ 1,301	$ 2,560
Received from counterparties	$ 1,685	$ 2,411

Derivatives and Fair Value Measurements - Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets (Detail) - Swaps [Member] - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Other Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Net Total		$ (845)
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ (122)	$ (3,532)
Prepaids and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	530
Deferred Charges and Other Assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ 736

Derivatives and Fair Value Measurements - Significant Other Observable Inputs (Detail) - Level 2 - Significant Other Observable Inputs [Member] - Swaps [Member] - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Assets (Liabilities)	$ (1,144)	$ 4,377
Prepaids and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	122	3,532
Deferred Charges and Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets		$ 845
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	(530)
Other Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ (736)

Common Stock - Additional Information (Detail)			1 Months Ended	3 Months Ended
Common Stock - Additional Information (Detail)	Mar. 31, 2017 shares	Mar. 29, 2017 USD ($)	Jan. 31, 2017	Mar. 31, 2017 shares
Conversion of stock conversion ratio			1
Value of common stock \| $		$ 150,000,000
Common stock issued through Restricted Stock/Unit Plan, and Management Incentive Plan				67,000
BNY Mellon Capital Markets, LLC [Member]
Common stock sold through agent	0

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	$ (26,064)	$ (50,101)
Long-term debt, less current maturities	1,564,132	1,549,983
Less: current maturities	(26,064)	(50,101)
Long-term debt, less current maturities	1,564,132	1,549,983
Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,385,315	1,375,080
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,385,315	1,375,080
Variable-rate bonds [Member] \| 2009 Series A, due 2039 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt, fair value	50,000	50,000
Carrying Amount [Member]
Long-term Debt, Current and Noncurrent Abstract
Long-term debt	1,590,196	1,600,084
Less: current maturities	(26,064)	(50,101)
Long-term debt, less current maturities	1,564,132	1,549,983
Less: current maturities	(26,064)	(50,101)
Long-term debt, less current maturities	1,564,132	1,549,983
Carrying Amount [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,385,315	1,375,080
Unamortized discount and debt issuance costs	(2,397)	(2,489)
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,385,315	1,375,080
Carrying Amount [Member] \| Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs	(485)	(516)
Centuri term loan/secured revolving credit facility	104,873	106,184
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(26,064)	(25,101)
Long-term debt, less current maturities	178,817	174,903
Less: current maturities	(26,064)	(25,101)
Long-term debt, less current maturities	178,817	174,903
Carrying Amount [Member] \| Centuri Secured Revolving Credit Facility [Member] \| Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Centuri term loan/secured revolving credit facility	51,054	41,185
Carrying Amount [Member] \| IDRBs [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt	197,603	197,511
Carrying Amount [Member] \| Centuri Term Loan Facility [Member] \| Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Centuri term loan/secured revolving credit facility	105,358	106,700
Carrying Amount [Member] \| Centuri Other Debt Obligations [Member] \| Centuri Construction Group Inc [Member]
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	48,954	52,635
Carrying Amount [Member] \| Debentures [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	1,172,712	1,197,569
Carrying Amount [Member] \| Debentures [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unamortized discount and debt issuance costs	(9,788)	(9,931)
Carrying Amount [Member] \| Debentures [Member] \| Notes, 4.45%, due 2020 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	125,000	125,000
Carrying Amount [Member] \| Debentures [Member] \| Notes, 6.1%, due 2041 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	125,000	125,000
Carrying Amount [Member] \| Debentures [Member] \| Notes, 3.875%, due 2022 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	250,000	250,000
Carrying Amount [Member] \| Debentures [Member] \| Notes, 4.875%, due 2043 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	250,000	250,000
Carrying Amount [Member] \| Debentures [Member] \| Notes, 3.8%, due 2046 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	300,000	300,000
Carrying Amount [Member] \| Debentures [Member] \| 8% Series, due 2026 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	75,000	75,000
Carrying Amount [Member] \| Debentures [Member] \| Medium-term notes, 7.59% series, due 2017 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable		25,000
Carrying Amount [Member] \| Debentures [Member] \| Medium-term notes, 7.78% series, due 2022 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	25,000	25,000
Carrying Amount [Member] \| Debentures [Member] \| Medium-term notes, 7.92% series, due 2027 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	25,000	25,000
Carrying Amount [Member] \| Debentures [Member] \| Medium-term notes, 6.76% series, due 2027 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Notes payable	7,500	7,500
Carrying Amount [Member] \| Debentures [Member] \| Revolving Credit Facility and Commercial Paper [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Line of credit facility	15,000	5,000
Carrying Amount [Member] \| Variable-rate bonds [Member] \| Tax-exempt Series A, due 2028 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt	50,000	50,000
Carrying Amount [Member] \| Variable-rate bonds [Member] \| 2003 Series A, due 2038 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt	50,000	50,000
Carrying Amount [Member] \| Variable-rate bonds [Member] \| 2008 Series A, due 2038 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt	50,000	50,000
Carrying Amount [Member] \| Variable-rate bonds [Member] \| 2009 Series A, due 2039 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt	50,000	50,000
Market Value [Member] \| Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Centuri term loan/secured revolving credit facility	105,944	106,819
Long-term Debt, Current and Noncurrent Abstract
Centuri other debt obligations	49,078	52,840
Market Value [Member] \| Centuri Secured Revolving Credit Facility [Member] \| Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Centuri term loan/secured revolving credit facility	51,144	41,292
Market Value [Member] \| Debentures [Member] \| Notes, 4.45%, due 2020 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	130,193	129,703
Market Value [Member] \| Debentures [Member] \| Notes, 6.1%, due 2041 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	150,255	149,734
Market Value [Member] \| Debentures [Member] \| Notes, 3.875%, due 2022 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	257,328	254,900
Market Value [Member] \| Debentures [Member] \| Notes, 4.875%, due 2043 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	264,968	266,793
Market Value [Member] \| Debentures [Member] \| Notes, 3.8%, due 2046 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	282,501	283,029
Market Value [Member] \| Debentures [Member] \| 8% Series, due 2026 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	94,822	94,691
Market Value [Member] \| Debentures [Member] \| Medium-term notes, 7.59% series, due 2017 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure		25,040
Market Value [Member] \| Debentures [Member] \| Medium-term notes, 7.78% series, due 2022 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	29,269	29,290
Market Value [Member] \| Debentures [Member] \| Medium-term notes, 7.92% series, due 2027 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	31,947	31,905
Market Value [Member] \| Debentures [Member] \| Medium-term notes, 6.76% series, due 2027 [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable, fair value disclosure	8,792	8,769
Market Value [Member] \| Debentures [Member] \| Revolving Credit Facility and Commercial Paper [Member] \| Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value	15,000	5,000
Market Value [Member] \| Variable-rate bonds [Member] \| Tax-exempt Series A, due 2028 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt, fair value	50,000	50,000
Market Value [Member] \| Variable-rate bonds [Member] \| 2003 Series A, due 2038 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt, fair value	50,000	50,000
Market Value [Member] \| Variable-rate bonds [Member] \| 2008 Series A, due 2038 [Member] \| Southwest Gas Corporation [Member]
Long-term Debt, Current and Noncurrent Abstract
Unsecured debt, fair value	$ 50,000	$ 50,000

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Parenthetical) (Detail) - Southwest Gas Corporation [Member]	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Debentures [Member] \| Medium-term notes, 7.59% series, due 2017 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.59%	7.59%
Debt instrument due date	Jan. 17, 2017	Jan. 17, 2017
Debentures [Member] \| Notes, 4.45%, due 2020 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.45%	4.45%
Debt instrument due date	Dec. 01, 2020	Dec. 01, 2020
Debentures [Member] \| Notes, 6.1%, due 2041 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.10%	6.10%
Debt instrument due date	Feb. 15, 2041	Feb. 15, 2041
Debentures [Member] \| Notes, 3.875%, due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.875%	3.875%
Debt instrument due date	Apr. 01, 2022	Apr. 01, 2022
Debentures [Member] \| Notes, 4.875%, due 2043 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%	4.875%
Debt instrument due date	Oct. 01, 2043	Oct. 01, 2043
Debentures [Member] \| Notes, 3.8%, due 2046 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.80%	3.80%
Debt instrument due date	Sep. 30, 2046	Sep. 30, 2046
Debentures [Member] \| 8% Series, due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	8.00%	8.00%
Debt instrument due date	Aug. 01, 2026	Aug. 01, 2026
Debentures [Member] \| Medium-term notes, 7.78% series, due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.78%	7.78%
Debt instrument due date	Feb. 03, 2022	Feb. 03, 2022
Debentures [Member] \| Medium-term notes, 7.92% series, due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.92%	7.92%
Debt instrument due date	Jun. 24, 2027	Jun. 24, 2027
Debentures [Member] \| Medium-term notes, 6.76% series, due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.76%	6.76%
Debt instrument due date	Sep. 24, 2027	Sep. 24, 2027
Variable-rate bonds [Member] \| Tax-exempt Series A, due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Dec. 01, 2028	Dec. 01, 2028
Variable-rate bonds [Member] \| 2003 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 01, 2038	Mar. 01, 2038
Variable-rate bonds [Member] \| 2008 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 01, 2038	Mar. 01, 2038
Market Value [Member] \| Variable-rate bonds [Member] \| 2009 Series A, due 2039 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Dec. 01, 2039	Dec. 01, 2039

Long-Term Debt - Additional Information (Detail)	3 Months Ended
Long-Term Debt - Additional Information (Detail)	Mar. 31, 2017 USD ($)
Centuri Construction Group Inc [Member] \| Secured Revolving Credit and Term Loan Facility [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 300,000,000
Credit facility expiration date	Oct. 31, 2019
Borrowings outstanding under facility	$ 156,000,000
Debt secured by assets	412,000,000
Southwest Gas Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	400,000,000
Line of credit designated as long term debt	150,000,000
Line of credit designated for working capital purposes	$ 250,000,000
Credit facility expiration date	Mar. 01, 2022
Southwest Gas Credit Facility [Member] \| Long-term Debt [Member]
Debt Instrument [Line Items]
Borrowings outstanding under facility	$ 15,000,000
Southwest Gas Credit Facility [Member] \| Short-term Debt [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 100,000,000
Credit facility expiration date	Mar. 31, 2022
Borrowings outstanding under facility	$ 0
Southwest Gas Credit Facility [Member] \| Before Amendment [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity	$ 300,000,000
Previous credit facility expiration date	Mar. 01, 2021
Southwest Gas Credit Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Applicable margin	1.00%
Southwest Gas Credit Facility [Member] \| Alternative Base Rate [Member]
Debt Instrument [Line Items]
Applicable margin	0.00%

Short-Term Debt - Additional Information (Detail) - Southwest Gas Credit Facility [Member]	3 Months Ended
	Mar. 31, 2017 USD ($)
Short-term Debt [Line Items]
Credit facility maximum borrowing capacity	$ 400,000,000
Credit facility expiration date	Mar. 01, 2022
Short-term Debt [Member]
Short-term Debt [Line Items]
Credit facility maximum borrowing capacity	$ 100,000,000
Credit facility expiration date	Mar. 31, 2022
Credit Facility [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Short term borrowings outstanding	$ 0
Minimum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Commitment fee	0.075%
Maximum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Commitment fee	0.20%
Alternative Base Rate [Member]
Short-term Debt [Line Items]
Applicable margin	0.00%
Alternative Base Rate [Member] \| Minimum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Applicable margin	0.00%
Alternative Base Rate [Member] \| Maximum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Applicable margin	0.50%
LIBOR [Member]
Short-term Debt [Line Items]
Applicable margin	1.00%
LIBOR [Member] \| Minimum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Applicable margin	0.75%
LIBOR [Member] \| Maximum [Member] \| Short-term Debt [Member]
Short-term Debt [Line Items]
Applicable margin	1.50%

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Schedule Of Stockholders Equity [Line Items]
Balance	$ 1,661,273
Balance	$ 22,590
Balance, shares	47,482,068
Common stock issuances	$ 6,306
Net income (loss)	69,263
Net income (loss)	69,005	$ 75,355	$ 146,705	$ 142,906
Redemption value adjustments	(1,288)
Foreign currency exchange translation adj.	213
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595	607	17	(379)
Amounts reclassified into net income	518	519	2,074	2,073
Dividends declared Common	(23,761)
Balance	1,713,119		1,713,119
Balance	$ 23,525		$ 23,525
Balance, shares	47,548,985		47,548,985
Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	$ 1,667,880
Net income (loss)	76,938
Net income (loss)	76,938	77,583	$ 118,778	110,287
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595	607	17	(379)
Amounts reclassified into net income	518	$ 519	2,074	$ 2,073
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations	(182,773)
Stock-based compensation	5,711
Dividends declared Common	(18,530)
Balance	1,550,339		1,550,339
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	$ 49,112
Balance, shares	47,482,000
Common stock issuances	$ 67
Common stock issuances, Shares	67,000
Other comprehensive income (loss):
Balance	$ 49,179		$ 49,179
Balance, shares	47,549,000		47,549,000
Common Stock [Member] \| Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	$ 49,112
Balance, shares	47,482,000
Other comprehensive income (loss):
Balance	$ 49,112		$ 49,112
Balance, shares	47,482,000		47,482,000
Additional Paid-in Capital [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	$ 903,123
Common stock issuances	6,239
Other comprehensive income (loss):
Balance	909,362		$ 909,362
Additional Paid-in Capital [Member] \| Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	897,346
Other comprehensive income (loss):
Stock-based compensation	5,906
Balance	903,252		903,252
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	(48,008)
Foreign currency exchange translation adj.	213
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595
Amounts reclassified into net income	518
Balance	(46,682)		(46,682)
Accumulated Other Comprehensive Income (Loss) [Member] \| Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	(45,639)
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595
Amounts reclassified into net income	518
Balance	(44,526)		(44,526)
Retained Earnings [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	759,263
Net income (loss)	69,308
Redemption value adjustments	(1,288)
Other comprehensive income (loss):
Dividends declared Common	(23,761)
Balance	803,522		803,522
Retained Earnings [Member] \| Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	767,061
Net income (loss)	76,938
Other comprehensive income (loss):
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations	(182,773)
Stock-based compensation	(195)
Dividends declared Common	(18,530)
Balance	642,501		642,501
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	22,590
Net income (loss) attributable to temporary equity	(258)
Redemption value adjustments	1,288
Foreign currency exchange translation adj attributable to temporary equity	7
Other comprehensive income (loss):
Centuri dividend to redeemable noncontrolling interest	(102)
Centuri dividend to redeemable noncontrolling interest	(102)
Balance	23,525		23,525
Non-controlling Interest [Member]
Schedule Of Stockholders Equity [Line Items]
Balance	(2,217)
Net income (loss)	(45)
Other comprehensive income (loss):
Balance	$ (2,262)		$ (2,262)

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Parenthetical) (Detail) - $ / shares	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Statement of Stockholders' Equity [Abstract]
Dividends declared Common, per share	$ 0.495	$ 0.450	$ 1.845	$ 1.665

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost, Before-Tax Amount	$ 334	$ 334	$ 1,335	$ 1,336
Translation adjustments, Before-Tax Amount	220	782	(401)	100
Translation adjustments, Tax (Expense) or Benefit	0	0
Amortization of net actuarial (gain)/loss, Before-Tax Amount	6,361	6,767	26,660	32,552
Foreign currency other comprehensive income (loss), Before-Tax Amount	220	782	(401)	100
Foreign currency other comprehensive income (loss), Tax (Expense) or Benefit	0	0	0	0
Net actuarial gain/(loss), Before-Tax Amount			(22,770)	(30,519)
Total other comprehensive income (loss), Before-Tax Amount	2,016	2,596	2,973	2,831
Total other comprehensive income (loss), Tax (Expense) or Benefit	(683)	(688)	(1,283)	(1,037)
Regulatory adjustment, Before-Tax Amount	(5,735)	(6,123)	(5,196)	(3,982)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	960	978	29	(613)
Amounts reclassified into net income, Before-Tax Amount	836	836	3,345	3,344
FSIRS other comprehensive income (loss), Before-Tax Amount	836	836	3,345	3,344
Net actuarial gain/(loss), Tax (Expense) or Benefit			8,652	11,597
Amortization of prior service cost, Tax (Expense) or Benefit	(127)	(127)	(507)	(507)
Amortization of net actuarial (gain)/loss, Tax (Expense) or Benefit	(2,417)	(2,571)	(10,131)	(12,370)
Regulatory adjustment, Tax (Expense) or Benefit	2,179	2,327	1,974	1,514
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(365)	(371)	(12)	234
Amounts reclassified into net income, Tax (Expense) or Benefit	(318)	(317)	(1,271)	(1,271)
FSIRS other comprehensive income (loss), Tax (Expense) or Benefit	(318)	(317)	(1,271)	(1,271)
Net actuarial gain/(loss), Net-of-Tax Amount			(14,118)	(18,922)
Amortization of prior service cost, Net-of-Tax Amount	207	207	828	829
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,196	16,529	20,182
Regulatory adjustment, Net-of-Tax Amount	(3,556)	(3,796)	(3,222)	(2,468)
Pension plans other comprehensive income (loss), Net-of-Tax Amount	595	607	17	(379)
Amounts reclassified into net income	518	519	2,074	2,073
FSIRS other comprehensive income (loss), Net-of-Tax Amount	518	519	2,074	2,073
Translation adjustments, Net-of-Tax Amount	220	782	(401)	100
Foreign currency other comprehensive income (loss), Net-of-Tax Amount	220	782	(401)	100
Total other comprehensive income (loss), net of tax	1,333	1,908	1,690	1,794
Southwest Gas Corporation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost, Before-Tax Amount	334
Amortization of net actuarial (gain)/loss, Before-Tax Amount	6,361
Total other comprehensive income (loss), Before-Tax Amount	1,796	1,814	3,374	2,731
Total other comprehensive income (loss), Tax (Expense) or Benefit	(683)	(688)	(1,283)	(1,037)
Regulatory adjustment, Before-Tax Amount	(5,735)
Amounts reclassified into net income, Before-Tax Amount	836
Amortization of prior service cost, Tax (Expense) or Benefit	(127)
Amortization of net actuarial (gain)/loss, Tax (Expense) or Benefit	(2,417)
Regulatory adjustment, Tax (Expense) or Benefit	2,179
Amounts reclassified into net income, Tax (Expense) or Benefit	(318)
Net actuarial gain/(loss), Net-of-Tax Amount			(14,118)	(18,922)
Amortization of prior service cost, Net-of-Tax Amount	207	207	828	829
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,196	16,529	20,182
Regulatory adjustment, Net-of-Tax Amount	(3,556)	(3,796)	(3,222)	(2,468)
Pension plans other comprehensive income (loss), Net-of-Tax Amount	595	607	17	(379)
Amounts reclassified into net income	518	519	2,074	2,073
FSIRS other comprehensive income (loss), Net-of-Tax Amount	518	519	2,074	2,073
Total other comprehensive income (loss), net of tax	$ 1,113	$ 1,126	$ 2,091	$ 1,694

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2017 USD ($)
Equity [Abstract]
Other comprehensive income loss, effective income tax rate	38.00%
Tax expense or benefit for currency translation adjustment	$ 0

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Additional Information (Detail) $ in Millions	Mar. 31, 2017 USD ($)
Equity [Abstract]
Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months	$ 2.1

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans Before-Tax	$ (57,613)
Translation adjustments, Defined Benefit Plans Before-Tax	0
Other comprehensive income before reclassifications, Defined Benefit Plans Before-Tax	0
Amortization of prior service cost, Defined Benefit Plans Before-Tax	334	$ 334	$ 1,335	$ 1,336
Amortization of net actuarial loss, Defined Benefit Plans Before-Tax	6,361	6,767	26,660	32,552
Regulatory adjustment, Defined Benefit Plans Before-Tax	(5,735)	(6,123)	(5,196)	(3,982)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	960	978	29	(613)
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans Before-Tax	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Before-Tax	960
Ending Balance AOCI March 31, 2017, Defined Benefit Plans Before-Tax	(56,653)		(56,653)
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans Tax (Expense) Benefit	21,893
Translation adjustments, Defined Benefit Plans Tax (Expense) Benefit	0
Other comprehensive income before reclassifications, Defined Benefit Plans Tax (Expense) Benefit	0
Amortization of prior service cost, Defined Benefit Plans Tax (Expense) Benefit	(127)	(127)	(507)	(507)
Amortization of net actuarial loss, Defined Benefit Plans Tax (Expense) Benefit	(2,417)	(2,571)	(10,131)	(12,370)
Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit	2,179	2,327	1,974	1,514
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(365)	(371)	(12)	234
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans Tax (Expense) Benefit	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Tax (Expense) Benefit	(365)
Ending Balance AOCI March 31, 2017, Defined Benefit Plans Tax (Expense) Benefit	21,528		21,528
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans After-Tax	(35,720)
Translation adjustments, Defined Benefit Plans After-Tax	0
Other comprehensive income before reclassifications, Defined Benefit Plans After-Tax	0
Amortization of prior service cost, Defined Benefit Plans After-Tax	207	207	828	829
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,196	16,529	20,182
Regulatory adjustment, Defined Benefit Plans After-Tax	(3,556)
Net defined benefit pension plans	595	607	17	(379)
Less: Translation adjustment attributable to redeemable noncontrolling interest, Defined Benefit Plans After-Tax	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans After-Tax	595
Ending Balance AOCI March 31, 2017, Defined Benefit Plans After-Tax	(35,125)		(35,125)
Beginning Balance AOCI December 31, 2016, FSIRS - Before-Tax	(15,999)
Translation adjustments, FSIRS - Before-Tax	0
Other comprehensive income before reclassifications, FSIRS - Before-Tax	0
FSIRS amounts reclassified from AOCI, FSIRS - Before-Tax	836	836	3,345	3,344
Net current period other comprehensive income (loss), FSIRS - Before-Tax	836	836	3,345	3,344
Less: Translation adjustment attributable to redeemable noncontrolling interest, FSIRS - Before-Tax	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Before-Tax	836
Ending Balance AOCI March 31, 2017, FSIRS - Before-Tax	(15,163)		(15,163)
Beginning Balance AOCI December 31, 2016, FSIRS - Tax (Expense) Benefit	6,080
Translation adjustments, FSIRS - Tax (Expense) Benefit	0
Other comprehensive income before reclassifications, FSIRS - Tax (Expense) Benefit	0
FSIRS amounts reclassified from AOCI, FSIRS - Tax (Expense) Benefit	(318)	(317)	(1,271)	(1,271)
Net current period other comprehensive income (loss), FSIRS - Tax (Expense) Benefit	(318)	(317)	(1,271)	(1,271)
Less: Translation adjustment attributable to redeemable noncontrolling interest, FSIRS - Tax (Expense) Benefit	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Tax (Expense) Benefit	(318)
Ending Balance AOCI March 31, 2017, FSIRS - Tax (Expense) Benefit	5,762		5,762
Beginning Balance AOCI December 31, 2016, FSIRS - After-Tax	(9,919)
Translation adjustments, FSIRS - After-Tax	0
Other comprehensive income before reclassifications	0
FSIRS amounts reclassified from AOCI, FSIRS - After-Tax	518	519	2,074	2,073
Net current period other comprehensive income (loss)	518	519	2,074	2,073
Less: Translation adjustment attributable to redeemable noncontrolling interest	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - After-Tax	518
Ending Balance AOCI March 31, 2017, FSIRS - After-Tax	(9,401)		(9,401)
Beginning Balance AOCI December 31, 2016, Foreign Currency Items Before-Tax	(2,369)
Translation adjustments, Foreign Currency Items Before-Tax	220	782	(401)	100
Other comprehensive income before reclassifications	220	782	(401)	100
FSIRS amounts reclassified from AOCI, Foreign Currency Items Before-Tax	0
Amortization of prior service cost, Foreign Currency Items Before-Tax	0
Amortization of net actuarial loss, Foreign Currency Items Before-Tax	0
Regulatory adjustment, Foreign Currency Items Before-Tax	0
Net current period other comprehensive income (loss)	220
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency Items Before-Tax	7
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings,Inc., Foreign Currency Items Before-Tax	213
Ending Balance AOCI March 31, 2017	(2,156)		(2,156)
Beginning Balance AOCI December 31, 2016, Foreign Currency items - Tax (Expense) Benefit	0
Translation adjustments, Foreign Currency items - Tax (Expense) Benefit	0	0
Other comprehensive income before reclassifications, Foreign Currency items - Tax (Expense) Benefit	0
FSIRS amounts reclassified from AOCI, Foreign Currency items - Tax (Expense) Benefit	0
Amortization of prior service cost ,Foreign Currency items - Tax (Expense) Benefit	0
Amortization of net actuarial loss, Foreign Currency items - Tax (Expense) Benefit	0
Regulatory adjustment, Foreign Currency items - Tax (Expense) Benefit	0
Net current period other comprehensive income (loss), Foreign Currency items - Tax (Expense) Benefit	0	0
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency items - Tax (Expense) Benefit	0
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings,Inc., Foreign Currency items - Tax (Expense) Benefit	0	0	0	0
Ending Balance AOCI March 31, 2017, Foreign Currency items - Tax (Expense) Benefit	0		0
Beginning Balance AOCI December 31, 2016, Foreign Currency items - After-Tax	(2,369)
Translation adjustments, Foreign Currency items - After-Tax	220	782	(401)	100
Other comprehensive income before reclassifications, Foreign Currency items - After-Tax	220	782	(401)	100
FSIRS amounts reclassified from AOCI, Foreign Currency items - After-Tax	0
Amortization of prior service cost, Foreign Currency items - After-Tax	0
Amortization of net actuarial loss, Foreign Currency items - After-Tax	0
Regulatory adjustment, Foreign Currency items - After-Tax	0
Net current period other comprehensive income (loss), Foreign Currency items - After-Tax	220
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency items - After-Tax	7
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings,Inc., Foreign Currency Items - After-Tax	213
Ending Balance AOCI March 31, 2017, Foreign Currency items - After-Tax	(2,156)		(2,156)
Beginning Balance AOCI December 31, 2016, AOCI	(48,008)
Translation adjustments, AOCI	220
Other comprehensive income before reclassifications, AOCI	220
Amounts reclassified into net income	518	519	2,074	2,073
Amortization of prior service cost, AOCI	207	207	828	829
Amortization of net actuarial loss	3,944	4,196	16,529	20,182
Regulatory adjustment, AOCI	(3,556)
Total other comprehensive income (loss), net of tax	1,333	1,908	1,690	1,794
Less: Translation adjustment attributable to redeemable noncontrolling interest, AOCI	7
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI	1,326
Ending Balance AOCI March 31, 2017, AOCI	(46,682)		(46,682)
Southwest Gas Corporation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans Before-Tax	(57,613)
Amortization of prior service cost, Defined Benefit Plans Before-Tax	334
Amortization of net actuarial loss, Defined Benefit Plans Before-Tax	6,361
Regulatory adjustment, Defined Benefit Plans Before-Tax	(5,735)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Before-Tax	960
Ending Balance AOCI March 31, 2017, Defined Benefit Plans Before-Tax	(56,653)		(56,653)
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans Tax (Expense) Benefit	21,893
Amortization of prior service cost, Defined Benefit Plans Tax (Expense) Benefit	(127)
Amortization of net actuarial loss, Defined Benefit Plans Tax (Expense) Benefit	(2,417)
Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit	2,179
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Tax (Expense) Benefit	(365)
Ending Balance AOCI March 31, 2017, Defined Benefit Plans Tax (Expense) Benefit	21,528		21,528
Beginning Balance AOCI December 31, 2016, Defined Benefit Plans After-Tax	(35,720)
Amortization of prior service cost, Defined Benefit Plans After-Tax	207	207	828	829
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,196	16,529	20,182
Regulatory adjustment, Defined Benefit Plans After-Tax	(3,556)
Net defined benefit pension plans	595	607	17	(379)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans After-Tax	595
Ending Balance AOCI March 31, 2017, Defined Benefit Plans After-Tax	(35,125)		(35,125)
Beginning Balance AOCI December 31, 2016, FSIRS - Before-Tax	(15,999)
FSIRS amounts reclassified from AOCI, FSIRS - Before-Tax	836
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Before-Tax	836
Ending Balance AOCI March 31, 2017, FSIRS - Before-Tax	(15,163)		(15,163)
Beginning Balance AOCI December 31, 2016, FSIRS - Tax (Expense) Benefit	6,080
FSIRS amounts reclassified from AOCI, FSIRS - Tax (Expense) Benefit	(318)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Tax (Expense) Benefit	(318)
Ending Balance AOCI March 31, 2017, FSIRS - Tax (Expense) Benefit	5,762		5,762
Beginning Balance AOCI December 31, 2016, FSIRS - After-Tax	(9,919)
FSIRS amounts reclassified from AOCI, FSIRS - After-Tax	518	519	2,074	2,073
Net current period other comprehensive income (loss)	518	519	2,074	2,073
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - After-Tax	518
Ending Balance AOCI March 31, 2017, FSIRS - After-Tax	(9,401)		(9,401)
Beginning Balance AOCI December 31, 2016, AOCI	(45,639)
Amounts reclassified into net income	518	519	2,074	2,073
Amortization of prior service cost, AOCI	207	207	828	829
Amortization of net actuarial loss	3,944	4,196	16,529	20,182
Regulatory adjustment, AOCI	(3,556)
Total other comprehensive income (loss), net of tax	1,113	$ 1,126	2,091	$ 1,694
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI	1,113
Ending Balance AOCI March 31, 2017, AOCI	$ (44,526)		$ (44,526)

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Parenthetical) (Detail)	3 Months Ended
	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income loss, effective income tax rate	38.00%
Southwest Gas Corporation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income loss, effective income tax rate	38.00%

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Amount Recognized Before Income Tax Associated with Defined Benefit Plans in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Recognized in AOCI	$ (56,653)	$ (57,613)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial (loss) gain	(424,612)	(430,973)
Prior service cost	(5,369)	(5,703)
Less: amount recognized in regulatory assets	373,328	379,063
Recognized in AOCI	$ (56,653)	$ (57,613)

Construction Services Redeemable Noncontrolling Interest - Additional Information (Detail) - Principal Previous Owners [Member] - Link-Line and WS Nicholls [Member]	1 Months Ended	3 Months Ended
	Oct. 31, 2014	Mar. 31, 2017
Noncontrolling Interest [Line Items]
Description of equity interest		In conjunction with the acquisition of the Canadian construction businesses in October 2014, the previous owners of the acquired companies currently hold a 3.4% equity interest in Centuri. The previous owners are able to exit their investment retained by requiring the purchase of a portion of their interest (a portion is already eligible for redemption). Incremental amounts will become eligible each year. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained is subject to the election beginning in July 2022.
Construction Services [Member]
Noncontrolling Interest [Line Items]
Percentage of earnings attribution by Centuri to previous owners	3.40%
Construction Services [Member] \| Maximum [Member]
Noncontrolling Interest [Line Items]
Percentage of retained interest may elect to sell to Centuri		100.00%

Construction Services Redeemable Noncontrolling Interest - Summary of Redeemable Noncontrolling Interest (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Redeemable Noncontrolling Interest [Line Items]
Balance	$ 22,590
Adjustment to redemption value	(1,288)
Balance	23,525
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Redeemable Noncontrolling Interest [Line Items]
Balance	22,590
Net income (loss) attributable to redeemable noncontrolling interest	(258)
Foreign currency exchange translation adjustment	7
Centuri dividend to redeemable noncontrolling interest	(102)
Adjustment to redemption value	1,288
Balance	$ 23,525

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Summary of Assets and Liabilities within Amounts Reported as Discontinued Operations - Construction Services in Condensed Consolidated Balance Sheet (Detail) - Construction Services [Member] - Southwest Gas Corporation [Member] $ in Thousands	Dec. 31, 2016 USD ($)
Assets:
Other property and investments	$ 233,774
Cash and cash equivalents	9,042
Accounts receivable, net of allowances	173,300
Prepaids and other current assets	10,470
Goodwill	129,888
Other noncurrent assets	22,897
Discontinued operations - construction services - assets	579,371
Liabilities:
Current maturities of long-term debt	25,101
Accounts payable	46,440
Other current liabilities	74,518
Long-term debt, less current maturities	174,903
Deferred income taxes and other deferred credits	59,653
Discontinued operations - construction services - liabilities	$ 380,615

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Components of Discontinued Operations - Construction Services Non-Owner Equity Amount in Condensed Consolidated Balance Sheet (Detail) - Southwest Gas Corporation [Member] $ in Thousands	Dec. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued operations - construction services non-owner equity	$ 15,983
Construction Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Construction services equity	(4,390)
Construction services noncontrolling interest	(2,217)
Construction services redeemable noncontrolling interest	22,590
Discontinued operations - construction services non-owner equity	$ 15,983

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation - Summary of Income Statement Components of Discontinued Operations - Construction Services in Condensed Consolidated Income Statements (Detail) - Southwest Gas Corporation [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Operating expenses:
Income (loss) before income taxes	$ (3,374)	$ 56,890	$ 52,804
Income tax expense (benefit)	(1,146)	21,030	20,185
Net income (loss)	(2,228)	35,860	32,619
Net income (loss) attributable to noncontrolling interests	(91)	1,105	1,126
Discontinued operations - construction services - net income (loss)	(2,137)	34,755	31,493
Construction Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Construction revenues	206,148	932,930	1,034,029
Operating expenses:
Construction expenses	193,382	831,041	917,235
Depreciation and amortization	14,615	41,054	57,479
Operating income (loss)	(1,849)	60,835	59,315
Other income (deductions)	(34)	1,227	883
Net interest deductions	1,491	5,172	7,394
Income (loss) before income taxes	(3,374)	56,890	52,804
Income tax expense (benefit)	(1,146)	21,030	20,185
Net income (loss)	(2,228)	35,860	32,619
Net income (loss) attributable to noncontrolling interests	(91)	1,105	1,126
Discontinued operations - construction services - net income (loss)	$ (2,137)	$ 34,755	$ 31,493