Southwest Gas 10-Q 8 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 28, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	SWX
Entity Registrant Name	SOUTHWEST GAS HOLDINGS, INC.
Entity Central Index Key	1,692,115
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		47,583,119

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Utility plant:
Gas plant	$ 6,349,303	$ 6,193,564
Less: accumulated depreciation	(2,202,909)	(2,172,966)
Acquisition adjustments, net	119	196
Construction work in progress	111,041	111,177
Net utility plant	4,257,554	4,131,971
Other property and investments	362,891	342,343
Current assets:
Cash and cash equivalents	29,702	28,066
Accounts receivable, net of allowances	281,882	285,145
Accrued utility revenue	33,600	76,200
Income taxes receivable, net	6,253	4,455
Deferred purchased gas costs	5,956	2,608
Prepaids and other current assets	126,192	136,833
Total current assets	483,585	533,307
Noncurrent assets:
Goodwill	143,583	139,983
Deferred income taxes	1,365	1,288
Deferred charges and other assets	416,261	432,234
Total noncurrent assets	561,209	573,505
Total assets	5,665,239	5,581,126
Capitalization:
Common stock	49,213	49,112
Additional paid-in capital	911,095	903,123
Accumulated other comprehensive income (loss), net	(44,962)	(48,008)
Retained earnings	801,222	759,263
Total Southwest Gas Holdings, Inc./Total Southwest Gas Corporation equity	1,716,568	1,663,490
Noncontrolling interest	(2,312)	(2,217)
Total equity	1,714,256	1,661,273
Redeemable noncontrolling interest	20,149	22,590
Long-term debt, less current maturities	1,685,698	1,549,983
Total capitalization	3,420,103	3,233,846
Current liabilities:
Current maturities of long-term debt	27,236	50,101
Short-term debt	2,500
Accounts payable	135,738	184,669
Customer deposits	71,195	72,296
Income taxes payable		1,909
Accrued general taxes	40,545	42,921
Accrued interest	17,150	17,939
Deferred purchased gas costs	20,628	90,476
Other current liabilities	175,043	168,064
Total current liabilities	490,035	628,375
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	891,217	840,653
Accumulated removal costs	310,000	308,000
Other deferred credits and other long-term liabilities	553,884	570,252
Total deferred income taxes and other credits	1,755,101	1,718,905
Total capitalization and liabilities	5,665,239	5,581,126
Southwest Gas Corporation [Member]
Utility plant:
Gas plant	6,349,303	6,193,564
Less: accumulated depreciation	(2,202,909)	(2,172,966)
Acquisition adjustments, net	119	196
Construction work in progress	111,041	111,177
Net utility plant	4,257,554	4,131,971
Other property and investments	113,326	108,569
Current assets:
Cash and cash equivalents	22,444	19,024
Accounts receivable, net of allowances	74,361	111,845
Accrued utility revenue	33,600	76,200
Income taxes receivable, net	4,902	4,455
Deferred purchased gas costs	5,956	2,608
Receivable from parent	288
Prepaids and other current assets	108,990	126,363
Total current assets	250,541	340,495
Noncurrent assets:
Goodwill	10,095	10,095
Deferred charges and other assets	399,628	410,625
Discontinued operations-construction services-assets		579,371
Total noncurrent assets	409,723	1,000,091
Total assets	5,031,144	5,581,126
Capitalization:
Common stock	49,112	49,112
Additional paid-in capital	904,715	897,346
Accumulated other comprehensive income (loss), net	(43,413)	(45,639)
Retained earnings	631,226	767,061
Total Southwest Gas Holdings, Inc./Total Southwest Gas Corporation equity	1,541,640	1,667,880
Discontinued operations-construction services non-owner equity		15,983
Total equity	1,541,640	1,667,880
Long-term debt, less current maturities	1,462,552	1,375,080
Total capitalization	3,004,192	3,058,943
Current liabilities:
Current maturities of long-term debt		25,000
Accounts payable	82,522	138,229
Customer deposits	71,195	72,296
Accrued general taxes	40,545	42,921
Accrued interest	16,826	17,395
Deferred purchased gas costs	20,628	90,476
Payable to parent	2,262
Other current liabilities	98,681	95,999
Total current liabilities	332,659	482,316
Deferred income taxes and other credits:
Deferred income taxes and investment tax credits	855,253	806,109
Accumulated removal costs	310,000	308,000
Other deferred credits and other long-term liabilities	529,040	545,143
Discontinued operations-construction services-liabilities		380,615
Total deferred income taxes and other credits	1,694,293	2,039,867
Total capitalization and liabilities	$ 5,031,144	$ 5,581,126

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 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	47,583,119	47,482,068
Common stock, outstanding	47,583,119	47,482,068

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating revenues:
Gas operating revenues	$ 260,162	$ 255,648	$ 722,764	$ 780,748	$ 1,263,428	$ 1,395,629
Construction revenues	300,307	292,100	492,442	498,248	1,133,272	1,074,168
Total operating revenues	560,469	547,748	1,215,206	1,278,996	2,396,700	2,469,797
Gas operating revenues	260,162	255,648	722,764	780,748	1,263,428	1,395,629
Operating expenses:
Net cost of gas sold	69,421	71,416	216,300	285,016	328,405	486,048
Operations and maintenance	103,060	98,744	212,210	199,541	414,393	397,886
Depreciation and amortization	58,082	72,559	130,560	147,919	271,773	283,608
Taxes other than income taxes	14,497	12,987	29,279	27,000	54,655	50,982
Construction expenses	272,001	263,926	463,957	457,308	1,031,072	955,332
Total operating expenses	517,061	519,632	1,052,306	1,116,784	2,100,298	2,173,856
Operating income	43,408	28,116	162,900	162,212	296,402	295,941
Other income and (expenses):
Net interest deductions	(18,655)	(18,221)	(37,369)	(35,942)	(75,087)	(72,127)
Other income (deductions)	2,047	2,470	5,912	4,191	11,190	4,636
Total other income and (expenses)	(16,608)	(15,751)	(31,457)	(31,751)	(63,897)	(67,491)
Income (loss) before income taxes	26,800	12,365	131,443	130,461	232,505	228,450
Income tax expense	8,679	3,266	44,317	46,007	76,778	81,508
Net income	18,121	9,099	87,126	84,454	155,727	146,942
Net income (loss) attributable to noncontrolling interests	257	156	(46)	65	903	1,168
Net income (loss)	$ 17,864	$ 8,943	$ 87,172	$ 84,389	$ 154,824	$ 145,774
Basic earnings per share	$ 0.38	$ 0.19	$ 1.83	$ 1.78	$ 3.26	$ 3.08
Diluted earnings per share	0.37	0.19	1.82	1.77	3.24	3.06
Dividends declared per share	$ 0.495	$ 0.450	$ 0.990	$ 0.900	$ 1.890	$ 1.710
Average number of common shares outstanding	47,571	47,473	47,550	47,455	47,516	47,347
Average shares outstanding (assuming dilution)	47,884	47,811	47,874	47,787	47,857	47,693
Southwest Gas Corporation [Member]
Operating revenues:
Gas operating revenues	$ 260,162	$ 255,648	$ 722,764	$ 780,748	$ 1,263,428	$ 1,395,629
Gas operating revenues	260,162	255,648	722,764	780,748	1,263,428	1,395,629
Operating expenses:
Net cost of gas sold	69,421	71,416	216,300	285,016	328,405	486,048
Operations and maintenance	102,501	98,744	211,180	199,541	413,363	397,886
Depreciation and amortization	46,254	57,232	107,449	117,977	222,935	224,845
Taxes other than income taxes	14,497	12,987	29,279	27,000	54,655	50,982
Total operating expenses	232,673	240,379	564,208	629,534	1,019,358	1,159,761
Operating income	27,489	15,269	158,556	151,214	244,070	235,868
Other income and (expenses):
Net interest deductions	(16,991)	(16,561)	(34,201)	(32,791)	(68,407)	(65,041)
Other income (deductions)	2,052	2,436	5,663	4,191	9,748	3,569
Total other income and (expenses)	(14,939)	(14,125)	(28,538)	(28,600)	(58,659)	(61,472)
Income (loss) before income taxes	12,550	1,144	130,018	122,614	185,411	174,396
Income tax expense	3,028	(1,214)	43,558	42,673	59,469	61,094
Net income	9,522	2,358	86,460	79,941	125,942	113,302
Discontinued operations-construction services, income before income taxes		11,221		7,847	45,669	54,054
Discontinued operations-construction services, Income tax expense		4,480		3,334	16,550	20,414
Discontinued operations-construction services, Income		6,741		4,513	29,119	33,640
Discontinued operations-construction services - Noncontrolling interests		156		65	949	1,168
Income-discontinued operations		6,585		4,448	28,170	32,472
Net income (loss)	$ 9,522	$ 8,943	$ 86,460	$ 84,389	$ 154,112	$ 145,774

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 18,121	$ 9,099	$ 87,126	$ 84,454	$ 155,727	$ 146,942
Defined benefit pension plans:
Net actuarial gain (loss)					(14,118)	(18,922)
Amortization of prior service cost	207	207	414	414	828	828
Amortization of net actuarial loss	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment	(3,556)	(3,796)	(7,112)	(7,592)	(2,982)	(1,436)
Net defined benefit pension plans	595	605	1,190	1,212	7	(482)
Forward-starting interest rate swaps:
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
Net forward-starting interest rate swaps	518	519	1,036	1,038	2,073	2,074
Foreign currency translation adjustments	629	70	849	852	158	(39)
Total other comprehensive income (loss), net of tax	1,742	1,194	3,075	3,102	2,238	1,553
Comprehensive income	19,863	10,293	90,201	87,556	157,965	148,495
Comprehensive income (loss) attributable to noncontrolling interests	279	159	(17)	94	908	1,166
Comprehensive income	19,584	10,134	90,218	87,462	157,057	147,329
Southwest Gas Corporation [Member]
Net income	9,522	2,358	86,460	79,941	125,942	113,302
Defined benefit pension plans:
Net actuarial gain (loss)					(14,118)	(18,922)
Amortization of prior service cost	207	207	414	414	828	828
Amortization of net actuarial loss	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment	(3,556)	(3,796)	(7,112)	(7,592)	(2,982)	(1,436)
Net defined benefit pension plans	595	605	1,190	1,212	7	(482)
Forward-starting interest rate swaps:
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
Net forward-starting interest rate swaps	518	519	1,036	1,038	2,073	2,074
Total other comprehensive income (loss), net of tax	1,113	1,124	2,226	2,250	2,080	1,592
Comprehensive income	10,635	3,482	88,686	82,191	128,022	114,894
Discontinued operations-construction services, net income		6,585		4,448	28,170	32,472
Discontinued operations-construction services, foreign currency translation adjustments		70		852	(691)	(39)
Discontinued operations-construction services, comprehensive income		6,655		5,300	27,479	32,433
Discontinued operations-construction services, comprehensive income (loss) attributable to noncontrolling interests		3		29	(24)	(2)
Comprehensive income attributable to discontinued operations-construction services		6,652		5,271	27,503	32,435
Comprehensive income	$ 10,635	$ 10,134	$ 88,686	$ 87,462	$ 155,525	$ 147,329

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
CASH FLOW FROM OPERATING ACTIVITIES:
Net income	$ 87,126	$ 84,454	$ 155,727	$ 146,942
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	130,560	147,919	271,773	283,608
Deferred income taxes	47,836	45,916	70,652	90,805
Changes in current assets and liabilities:
Accounts receivable, net of allowances	3,545	52,907	(19,266)	7,039
Accrued utility revenue	42,600	42,200	(1,100)	(700)
Deferred purchased gas costs	(73,196)	84,289	(111,627)	102,834
Accounts payable	(50,447)	(33,358)	4,606	1,622
Accrued taxes	(6,100)	(12,121)	32,361	(28,140)
Other current assets and liabilities	20,390	7,761	(14,803)	22,696
Gains on sale	(1,427)	(2,742)	(5,833)	(3,281)
Changes in undistributed stock compensation	7,731	3,514	9,673	4,916
AFUDC	(1,109)	(1,282)	(2,116)	(3,157)
Changes in other assets and deferred charges	(11,521)	223	5,216	1,296
Changes in other liabilities and deferred credits	2,204	(2,502)	(13,741)	5,407
Net cash provided by operating activities	198,192	417,178	381,522	631,887
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(262,234)	(264,872)	(526,893)	(549,232)
Acquisition of businesses, net of cash acquired		(17,000)		(17,000)
Changes in customer advances	(1,430)	2,152	4,318	10,763
Miscellaneous inflows	6,905	4,126	15,818	7,588
Net cash used in investing activities	(256,759)	(275,594)	(506,757)	(547,881)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net	(96)	487	(111)	15,170
Dividends paid	(44,949)	(40,583)	(87,683)	(78,830)
Centuri distribution to redeemable noncontrolling interest	(204)	(99)	(544)	(198)
Issuance of long-term debt, net	80,579	96,128	408,397	138,779
Retirement of long-term debt	(60,041)	(52,966)	(262,348)	(162,530)
Change in credit facility and commercial paper	87,000	(147,500)	89,500	(27,500)
Change in short-term debt	2,500	(18,000)	2,500
Principal payments on capital lease obligations	(573)	(835)	(1,092)	(1,533)
Withholding remittance-share-based compensation	(3,120)	(1,968)	(3,271)	(3,766)
Other	(1,036)	(124)	(2,481)	451
Net cash provided by (used in) financing activities	60,060	(165,460)	142,867	(119,957)
Effects of currency translation on cash and cash equivalents	143	5	(56)	(832)
Change in cash and cash equivalents	1,636	(23,871)	17,576	(36,783)
Cash and cash equivalents at beginning of period	28,066	35,997	12,126	48,909
Cash and cash equivalents at end of period	29,702	12,126	29,702	12,126
Supplemental information:
Interest paid, net of amounts capitalized	35,182	33,224	69,398	65,634
Income taxes paid (received)	3,043	4,737	(20,726)	19,483
Southwest Gas Corporation [Member]
CASH FLOW FROM OPERATING ACTIVITIES:
Net Income	86,460	84,454	155,061	146,942
Net income	86,460	79,941	125,942	113,302
Income (loss) from discontinued operations		4,513	29,119	33,640
Income from continuing operations	86,460	79,941	125,942	113,302
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	107,449	117,977	222,935	224,845
Deferred income taxes	46,874	40,592	74,241	83,140
Changes in current assets and liabilities:
Accounts receivable, net of allowances	37,484	79,188	(973)	22,324
Accrued utility revenue	42,600	42,200	(1,100)	(700)
Deferred purchased gas costs	(73,196)	84,289	(111,627)	102,834
Accounts payable	(55,707)	(42,681)	3,157	(3,529)
Accrued taxes	(2,823)	(6,456)	23,024	(17,334)
Other current assets and liabilities	24,265	4,791	(14,022)	11,614
Changes in undistributed stock compensation	6,931	3,514	8,873	4,916
AFUDC	(1,109)	(1,282)	(2,116)	(3,157)
Changes in other assets and deferred charges	(11,801)	49	4,761	603
Changes in other liabilities and deferred credits	1,695	(2,502)	(14,250)	5,407
Net cash provided by operating activities	209,122	399,620	318,845	544,265
CASH FLOW FROM INVESTING ACTIVITIES:
Construction expenditures and property additions	(224,085)	(214,424)	(466,780)	(474,596)
Changes in customer advances	(1,430)	2,152	4,318	10,763
Miscellaneous inflows	1,354	1,790	2,546	3,660
Dividends received		2,801	9,660	5,602
Net cash used in investing activities	(224,161)	(207,681)	(450,256)	(454,571)
CASH FLOW FROM FINANCING ACTIVITIES:
Issuance of common stock, net		487	(15)	15,170
Dividends paid	(39,896)	(40,583)	(82,630)	(78,830)
Issuance of long-term debt, net			296,469
Retirement of long-term debt	(25,000)		(149,855)	(20,000)
Change in credit facility and commercial paper	87,000	(147,500)	89,500	(27,500)
Change in short-term debt		(18,000)
Withholding remittance-share-based compensation	(3,120)	(1,968)	(3,271)	(3,766)
Other	(525)	(124)	(1,970)	502
Net cash provided by (used in) financing activities	18,459	(207,688)	148,228	(114,424)
Net cash provided by discontinued operating activities		17,558	73,607	87,622
Net cash used in discontinued investing activities		(67,913)	(23,903)	(93,310)
Net cash provided by (used in) discontinued financing activities		42,228	(46,962)	(5,533)
Effects of currency translation on cash and cash equivalents		5	(199)	(832)
Change in cash and cash equivalents	3,420	(23,871)	19,360	(36,783)
Change in cash and cash equivalents of discontinued operations included in discontinued operations construction services assets		8,122	(2,543)	12,053
Change in cash and cash equivalents of continuing operations	3,420	(15,749)	16,817	(24,730)
Cash and cash equivalents at beginning of period	19,024	21,376	5,627	30,357
Cash and cash equivalents at end of period	22,444	5,627	22,444	5,627
Supplemental information:
Interest paid, net of amounts capitalized	32,205	30,485	63,221	60,101
Income taxes paid (received)	$ 19	$ 1,893	$ (32,885)	$ (3,063)

Nature of Operations and Basis

Nature of Operations and Basis of Presentation	6 Months Ended
	Jun. 30, 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. one-for-one 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. 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 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. Cash and Cash Equivalents. Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $1.6 million and $2.5 million, during the first six 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. 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 previous 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. (In thousands of dollars) Natural Gas Construction Consolidated December 31, 2016 $ 10,095 $ 129,888 $ 139,983 Foreign currency translation adjustment — 3,600 3,600 June 30, 2017 $ 10,095 $ 133,488 $ 143,583 Intercompany Transactions Note 3—Segment Information June 30, 2017 December 31, 2016 Centuri accounts receivable for services provided to Southwest $ 10,265 $ 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. June 30, 2017 December 31, 2016 Centuri property and equipment $ 478,247 $ 451,114 Centuri accumulated provision for depreciation and amortization (240,182 ) (228,374 ) Net cash surrender value of COLI policies 111,523 106,744 Other property 13,303 12,859 Total $ 362,891 $ 342,343 Other Income (Deductions). Three Months Ended Six Months Ended Twelve Months Ended June 30 June 30 June 30 2017 2016 2017 2016 2017 2016 Southwest Gas Corporation - natural gas operations segment: Change in COLI policies $ 1,900 $ 2,200 $ 4,700 $ 3,100 $ 9,000 $ 1,300 Interest income 614 390 1,178 757 2,269 1,766 Equity AFUDC 633 750 1,109 1,282 2,116 3,157 Miscellaneous income and (expense) (1,095 ) (904 ) (1,324 ) (948 ) (3,637 ) (2,654 ) Southwest Gas Corporation - total other income (deductions) 2,052 2,436 5,663 4,191 9,748 3,569 Construction services segment: Interest income 1 1 1 1 1 414 Foreign transaction gain (loss) (197 ) (9 ) (198 ) (19 ) (201 ) (271 ) Miscellaneous income and (expense) 190 42 445 18 1,641 924 Centuri - total other income (deductions) (6 ) 34 248 — 1,441 1,067 Corporate and administrative 1 — 1 — 1 — Consolidated Southwest Gas Holdings, Inc. - total other income (deductions) $ 2,047 $ 2,470 $ 5,912 $ 4,191 $ 11,190 $ 4,636 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. 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 the 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 being separately addressed by the P&U Task Force. As of June 30, 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

Components of Net Periodic Bene

Components of Net Periodic Benefit Cost	6 Months Ended
	Jun. 30, 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 June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 5,848 $ 5,708 $ 11,696 $ 11,417 $ 23,112 $ 23,979 Interest cost 11,521 11,507 23,041 23,013 46,055 45,127 Expected return on plan assets (13,799 ) (14,139 ) (27,598 ) (28,279 ) (55,877 ) (57,183 ) Amortization of net actuarial loss 6,001 6,316 12,002 12,633 24,635 29,005 Net periodic benefit cost $ 9,571 $ 9,392 $ 19,141 $ 18,784 $ 37,925 $ 40,928 SERP Period Ended June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 77 $ 83 $ 155 $ 165 $ 321 $ 325 Interest cost 471 465 942 930 1,871 1,778 Amortization of net actuarial loss 360 346 720 692 1,411 1,338 Net periodic benefit cost $ 908 $ 894 $ 1,817 $ 1,787 $ 3,603 $ 3,441 PBOP Period Ended June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 367 $ 375 $ 734 $ 749 $ 1,484 $ 1,569 Interest cost 808 795 1,616 1,591 3,205 3,091 Expected return on plan assets (839 ) (787 ) (1,679 ) (1,575 ) (3,253 ) (3,307 ) Amortization of prior service costs 334 334 668 668 1,335 1,336 Amortization of net actuarial loss — 104 — 208 209 380 Net periodic benefit cost $ 670 $ 821 $ 1,339 $ 1,641 $ 2,980 $ 3,069

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 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 Statements of Income, 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 Other Total Three months ended June 30, 2017 Revenues from external customers $ 260,162 $ 277,384 $ — $ 537,546 Intersegment revenues — 22,923 — 22,923 Total $ 260,162 $ 300,307 $ — $ 560,469 Segment net income (loss) $ 9,522 $ 8,716 $ (374 ) $ 17,864 Three months ended June 30, 2016 Revenues from external customers $ 255,648 $ 266,343 $ — $ 521,991 Intersegment revenues — 25,757 — 25,757 Total $ 255,648 $ 292,100 $ — $ 547,748 Segment net income $ 2,358 $ 6,585 $ — $ 8,943 Natural Gas Construction Other Total Six months ended June 30, 2017 Revenues from external customers $ 722,764 $ 448,223 $ — $ 1,170,987 Intersegment revenues — 44,219 — 44,219 Total $ 722,764 $ 492,442 $ — $ 1,215,206 Segment net income (loss) $ 86,460 $ 1,382 $ (670 ) $ 87,172 Six months ended June 30, 2016 Revenues from external customers $ 780,748 $ 450,304 $ — $ 1,231,052 Intersegment revenues — 47,944 — 47,944 Total $ 780,748 $ 498,248 $ — $ 1,278,996 Segment net income $ 79,941 $ 4,448 $ — $ 84,389 Natural Gas Construction Other Total Twelve months ended June 30, 2017 Revenues from external customers $ 1,263,428 $ 1,038,876 $ — $ 2,302,304 Intersegment revenues — 94,396 — 94,396 Total $ 1,263,428 $ 1,133,272 $ — $ 2,396,700 Segment net income (loss) $ 125,942 $ 29,552 $ (670 ) $ 154,824 Twelve months ended June 30, 2016 Revenues from external customers $ 1,395,629 $ 964,973 $ — $ 2,360,602 Intersegment revenues — 109,195 — 109,195 Total $ 1,395,629 $ 1,074,168 $ — $ 2,469,797 Segment net income $ 113,302 $ 32,472 $ — $ 145,774

Derivatives and Fair Value Meas

Derivatives and Fair Value Measurements	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Derivatives and Fair Value Measurements	Note 4 – Derivatives and Fair Value Measurements Derivatives. 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 July 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): June 30, 2017 December 31, 2016 Contract notional amounts 11,035 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-, six-, and twelve-month periods ended June 30, 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 Six Months Ended Twelve Months Ended Location of Gain or (Loss) June 30 June 30 June 30 Instrument Recognized in Income on Derivative 2017 2016 2017 2016 2017 2016 Swaps Net cost of gas sold $ (1,168 ) $ 5,537 $ (6,305 ) $ 4,325 $ (5,624 ) $ (1,866 ) Swaps Net cost of gas sold 1,168 * (5,537 )* 6,305 * (4,325 )* 5,624 * 1,866 * 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: June 30, 2017 Instrument Balance Sheet Location Asset Liability Net Total Swaps Other current liabilities $ 25 $ (1,575 ) $ (1,550 ) Swaps Other deferred credits 29 (681 ) (652 ) Total $ 54 $ (2,256 ) $ (2,202 ) December 31, 2016 Instrument Balance Sheet Location Asset Liability 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 Six Months Ended Twelve Months Ended (Thousands of dollars) June 30, 2017 June 30, 2017 June 30, 2017 Paid to counterparties $ 111 $ 1,412 $ 2,512 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). June 30, 2017 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 1,550 Swaps Deferred charges and other assets 652 December 31, 2016 Balance Sheet Location Net Total Swaps Other deferred credits $ (845 ) Swaps Other current liabilities (3,532 ) Fair Value Measurements. 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) June 30, December 31, Assets at fair value: Prepaids and other current assets - Swaps $ — $ 3,532 Deferred charges and other assets - Swaps — 845 Liabilities at fair value: Other current liabilities - Swaps (1,550 ) — Other deferred credits - Swaps (652 ) — Net Assets (Liabilities) $ (2,202 ) $ 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

Common Stock	6 Months Ended
	Jun. 30, 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 six months ended June 30, 2017, the Company issued approximately 101,000 shares of common stock through the Restricted Stock/Unit Plan and Management Incentive Plan.

Long-Term Debt

Long-Term Debt	6 Months Ended
	Jun. 30, 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 June 30, 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/market rates. The fair values of Southwest’s debentures, senior notes, and fixed-rate IDRBs were determined utilizing a market-based valuation approach, where fair values are determined based on evaluated pricing data, such as broker quotes and yields for similar securities adjusted for observable differences. Significant inputs used in the valuation generally include benchmark yield curves, credit ratings and issuer spreads. The external credit rating, coupon rate, and maturity of each security are considered in the valuation, as applicable. The fair values of debentures 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. Because 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. June 30, 2017 December 31, 2016 Carrying Fair Carrying Fair Amount Value Amount Value (Thousands of dollars) Southwest Gas Corporation: Debentures: Notes, 4.45%, due 2020 $ 125,000 $ 130,821 $ 125,000 $ 129,703 Notes, 6.1%, due 2041 125,000 155,466 125,000 149,734 Notes, 3.875%, due 2022 250,000 259,368 250,000 254,900 Notes, 4.875%, due 2043 250,000 268,728 250,000 266,793 Notes, 3.8%, due 2046 300,000 284,172 300,000 283,029 8% Series, due 2026 75,000 96,783 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 29,356 25,000 29,290 Medium-term notes, 7.92% series, due 2027 25,000 32,320 25,000 31,905 Medium-term notes, 6.76% series, due 2027 7,500 8,914 7,500 8,769 Unamortized discount and debt issuance costs (9,644 ) (9,931 ) 1,172,856 1,197,569 Revolving credit facility and commercial paper 92,000 92,000 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 (2,304 ) (2,489 ) 197,696 197,511 Less: current maturities — (25,000 ) Long-term debt, less current maturities - Southwest Gas Corporation $ 1,462,552 $ 1,375,080 Centuri: Centuri term loan facility $ 105,559 105,641 $ 106,700 106,819 Unamortized debt issuance costs (427 ) (516 ) 105,132 106,184 Centuri secured revolving credit facility 99,943 100,091 41,185 41,292 Centuri other debt obligations 45,307 45,589 52,635 52,840 Less: current maturities (27,236 ) (25,101 ) Long-term debt, less current maturities - Centuri $ 223,146 $ 174,903 Consolidated Southwest Gas Holdings, Inc.: Southwest Gas Corporation long-term debt $ 1,462,552 $ 1,400,080 Centuri long-term debt 250,382 200,004 Less: current maturities (27,236 ) (50,101 ) Long-term debt, less current maturities - Southwest Gas Holdings, Inc. $ 1,685,698 $ 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 June 30, 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 June 30, 2017, $92 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 June 30, 2017, $206 million in borrowings were outstanding on the Centuri facility. Centuri assets securing the facility at June 30, 2017 totaled $501 million.

Short-Term Debt

Short-Term Debt	6 Months Ended
	Jun. 30, 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 1.50% 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 0.200% per annum. At June 30, 2017, $2.5 million was outstanding on this facility.

Equity, Other Comprehensive Inc

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income	6 Months Ended
	Jun. 30, 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 six months ended June 30, 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 DECEMBER 31, 2016 47,482 $ 49,112 $ 903,123 $ (48,008 ) $ 759,263 $ (2,217 ) $ 1,661,273 $ 22,590 Common stock issuances 101 101 7,972 8,073 Net income (loss) 87,172 (95 ) 87,077 49 Redemption value adjustments 2,315 2,315 (2,315 ) Foreign currency exchange translation adj. 820 820 29 Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax 1,190 1,190 Amounts reclassified to net income, net of tax (FSIRS) 1,036 1,036 Centuri dividend to redeemable noncontrolling interest (204 ) Dividends declared Common: $0.99 per share (47,528 ) (47,528 ) JUNE 30, 2017 47,583 $ 49,213 $ 911,095 $ (44,962 ) $ 801,222 $ (2,312 ) $ 1,714,256 $ 20,149 The table below provides details of activity in equity for Southwest Gas Corporation during the six months ended June 30, 2017. Effective in January 2017, Southwest became a 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 Common Stock Additional Accumulated 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 86,460 86,460 Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized ben efit plan cost, net of tax 1,190 1,190 Amounts reclassified to net income,net of tax (FSIRS) 1,036 1,036 Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations (182,773 ) (182,773 ) Stock-based compensation (a) 7,369 (392 ) 6,977 Dividends declared to Southwest Gas Holdings, Inc. (39,130 ) (39,130 ) JUNE 30, 2017 47,482 $ 49,112 $ 904,715 $ (43,413 ) $ 631,226 $ 1,541,640 (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 Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Thousands of dollars) Three Months Ended June 30, 2017 Three Months Ended June 30, 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 6,766 (2,572 ) 4,194 Regulatory adjustment (5,735 ) 2,179 (3,556 ) (6,123 ) 2,327 (3,796 ) Pension plans other comprehensive income (loss) 960 (365 ) 595 977 (372 ) 605 FSIRS (designated hedging activities): Amounts reclassifed into net income 836 (318 ) 518 837 (318 ) 519 FSIRS other comprehensive income 836 (318 ) 518 837 (318 ) 519 Total other comprehensive income (loss) - Southwest Gas Corporation 1,796 (683 ) 1,113 1,814 (690 ) 1,124 Foreign currency translation adjustments: Translation adjustments 629 — 629 70 — 70 Foreign currency other comprehensive income (loss) 629 — 629 70 — 70 Total other comprehensive income (loss) - Southwest Gas Holdings, Inc. $ 2,425 $ (683 ) $ 1,742 $ 1,884 $ (690 ) $ 1,194 Six Months Ended June 30, 2017 Six Months Ended June 30, 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 $ 668 $ (254 ) $ 414 $ 668 $ (254 ) $ 414 Amortization of net actuarial (gain)/loss 12,722 (4,834 ) 7,888 13,533 (5,143 ) 8,390 Regulatory adjustment (11,470 ) 4,358 (7,112 ) (12,246 ) 4,654 (7,592 ) Pension plans other comprehensive income (loss) 1,920 (730 ) 1,190 1,955 (743 ) 1,212 FSIRS (designated hedging activities): Amounts reclassifed into net income 1,672 (636 ) 1,036 1,673 (635 ) 1,038 FSIRS other comprehensive income 1,672 (636 ) 1,036 1,673 (635 ) 1,038 Total other comprehensive income (loss)—Southwest Gas Corporation 3,592 (1,366 ) 2,226 3,628 (1,378 ) 2,250 Foreign currency translation adjustments: Translation adjustments 849 — 849 852 — 852 Foreign currency other comprehensive income (loss) 849 — 849 852 — 852 Total other comprehensive income (loss)—Southwest Gas Holdings, Inc. $ 4,441 $ (1,366 ) $ 3,075 $ 4,480 $ (1,378 ) $ 3,102 Twelve Months Ended June 30, 2017 Twelve Months Ended June 30, 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 (508 ) 828 Amortization of net actuarial (gain)/loss 26,255 (9,976 ) 16,279 30,723 (11,675 ) 19,048 Regulatory adjustment (4,808 ) 1,826 (2,982 ) (2,318 ) 882 (1,436 ) Pension plans other comprehensive income (loss) 12 (5 ) 7 (778 ) 296 (482 ) FSIRS (designated hedging activities): Amounts reclassifed into net income 3,344 (1,271 ) 2,073 3,345 (1,271 ) 2,074 FSIRS other comprehensive income (loss) 3,344 (1,271 ) 2,073 3,345 (1,271 ) 2,074 Total other comprehensive income (loss)—Southwest Gas Corporation 3,356 (1,276 ) 2,080 2,567 (975 ) 1,592 Foreign currency translation adjustments: Translation adjustments 158 — 158 (39 ) — (39 ) Foreign currency other comprehensive income (loss) 158 — 158 (39 ) — (39 ) Total other comprehensive income (loss)—Southwest Gas Holdings, Inc. $ 3,514 $ (1,276 ) $ 2,238 $ 2,528 $ (975 ) $ 1,553 (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 June 30, 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 After-Tax Before-Tax Tax After-Tax Before-Tax Tax 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 — — — — — — 849 — 849 849 Other comprehensive income before reclassifications — — — — — — 849 — 849 849 FSIRS amounts reclassified from AOCI (1) — — — 1,672 (636 ) 1,036 — — — 1,036 Amortization of prior service cost (2) 668 (254 ) 414 — — — — — — 414 Amortization of net actuarial loss (2) 12,722 (4,834 ) 7,888 — — — — — — 7,888 Regulatory adjustment (3) (11,470 ) 4,358 (7,112 ) — — — — — — (7,112 ) Net current period other comprehensive income (loss) 1,920 (730 ) 1,190 1,672 (636 ) 1,036 849 — 849 3,075 Less: Translation adjustment attributable to redeemable noncontrolling interest — — — — — — 29 — 29 29 Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc. 1,920 (730 ) 1,190 1,672 (636 ) 1,036 820 — 820 3,046 Ending Balance AOCI June 30, 2017 $ (55,693 ) $ 21,163 $ (34,530 ) $ (14,327 ) $ 5,444 $ (8,883 ) $ (1,549 ) $ — $ (1,549 ) $ (44,962 ) (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 (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 After-Tax Before-Tax Tax 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) — — — 1,672 (636 ) 1,036 1,036 Amortization of prior service cost (6) 668 (254 ) 414 — — — 414 Amortization of net actuarial loss (6) 12,722 (4,834 ) 7,888 — — — 7,888 Regulatory adjustment (7) (11,470 ) 4,358 (7,112 ) — — — (7,112 ) Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation 1,920 (730 ) 1,190 1,672 (636 ) 1,036 2,226 Ending Balance AOCI June 30, 2017 $ (55,693 ) $ 21,163 $ (34,530 ) $ (14,327 ) $ 5,444 $ (8,883 ) $ (43,413 ) (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 (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) June 30, 2017 December 31, 2016 (Thousands of dollars) Net actuarial (loss) gain $ (418,251 ) $ (430,973 ) Prior service cost (5,035 ) (5,703 ) Less: amount recognized in regulatory assets 367,593 379,063 Recognized in AOCI $ (55,693 ) $ (57,613 )

Construction Services Redeemabl

Construction Services Redeemable Noncontrolling Interest	6 Months Ended
	Jun. 30, 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 hold a 3.4% equity interest in Centuri as of June 30, 2017. The terms of the agreement subject to the 3.4% interest permit the previous owners (when eligible) to exit their investment retained by requiring (if elected) the purchase of a portion of their interest based on an eligibility timeline, with incremental amounts subject to the election each year. The redemption price of the redeemable noncontrolling interest in accordance with the terms of the agreement is at fair value. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained would be subject to the election beginning in July 2022. Due to the ability of the noncontrolling parties to redeem their interest for cash under the eligibility timeline, their interest is presented on the Company’s Condensed Consolidated Balance Sheet at June 30, 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 (Thousands of dollars): Balance, December 31, 2016 $ 22,590 Net income (loss) attributable to redeemable noncontrolling interest 49 Foreign currency exchange translation adjustment 29 Centuri dividend to redeemable noncontrolling interest (204 ) Adjustment to redemption value (2,315 ) Balance, June 30, 2017 $ 20,149

Reorganization Impacts - Discon

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation	6 Months Ended
	Jun. 30, 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: Results of Construction Services Three Six Twelve Twelve Months Ended Months Ended Months Ended Months Ended (Thousands of dollars) June 30, 2016 June 30, 2016 June 30, 2017 June 30, 2016 Construction revenues $ 292,100 $ 498,248 $ 640,830 $ 1,074,168 Operating expenses: Construction expenses 263,926 457,308 567,115 955,332 Depreciation and amortization 15,327 29,942 25,727 58,763 Operating income 12,847 10,998 47,988 60,073 Other income (deductions) 34 — 1,193 1,067 Net interest deductions 1,660 3,151 3,512 7,086 Income before income taxes 11,221 7,847 45,669 54,054 Income tax expense (benefit) 4,480 3,334 16,550 20,414 Net income 6,741 4,513 29,119 33,640 Net income attributable to noncontrolling interests 156 65 949 1,168 Discontinued operations - construction services - net income $ 6,585 $ 4,448 $ 28,170 $ 32,472

Nature of Operations and Basi17

Nature of Operations and Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations. one-for-one 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	Basis of Presentation. Form 10-Q, Note 10 – Reorganization Impacts – Discontinued Operations Solely Related to Southwest Gas Corporation non-current 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.
Cash and Cash Equivalents	Cash and Cash Equivalents. Significant non-cash investing and financing activities for the natural gas operations segment included the following: Upon contract expiration, customer advances of approximately $1.6 million and $2.5 million, during the first six 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	Adoption of Accounting Standards Update (“ASU”) No. 2016-09. 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 previous 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. (In thousands of dollars) Natural Gas Construction Consolidated December 31, 2016 $ 10,095 $ 129,888 $ 139,983 Foreign currency translation adjustment — 3,600 3,600 June 30, 2017 $ 10,095 $ 133,488 $ 143,583
Intercompany Transactions	Intercompany Transactions Note 3—Segment Information June 30, 2017 December 31, 2016 Centuri accounts receivable for services provided to Southwest $ 10,265 $ 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. June 30, 2017 December 31, 2016 Centuri property and equipment $ 478,247 $ 451,114 Centuri accumulated provision for depreciation and amortization (240,182 ) (228,374 ) Net cash surrender value of COLI policies 111,523 106,744 Other property 13,303 12,859 Total $ 362,891 $ 342,343
Other Income (Deductions)	Other Income (Deductions). Three Months Ended Six Months Ended Twelve Months Ended June 30 June 30 June 30 2017 2016 2017 2016 2017 2016 Southwest Gas Corporation - natural gas operations segment: Change in COLI policies $ 1,900 $ 2,200 $ 4,700 $ 3,100 $ 9,000 $ 1,300 Interest income 614 390 1,178 757 2,269 1,766 Equity AFUDC 633 750 1,109 1,282 2,116 3,157 Miscellaneous income and (expense) (1,095 ) (904 ) (1,324 ) (948 ) (3,637 ) (2,654 ) Southwest Gas Corporation - total other income (deductions) 2,052 2,436 5,663 4,191 9,748 3,569 Construction services segment: Interest income 1 1 1 1 1 414 Foreign transaction gain (loss) (197 ) (9 ) (198 ) (19 ) (201 ) (271 ) Miscellaneous income and (expense) 190 42 445 18 1,641 924 Centuri - total other income (deductions) (6 ) 34 248 — 1,441 1,067 Corporate and administrative 1 — 1 — 1 — Consolidated Southwest Gas Holdings, Inc. - total other income (deductions) $ 2,047 $ 2,470 $ 5,912 $ 4,191 $ 11,190 $ 4,636 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
Recently Issued Accounting Standards Updates	Recently Issued Accounting Standards Updates. 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 the 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 being separately addressed by the P&U Task Force. As of June 30, 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

Nature of Operations and Basi18

Nature of Operations and Basis of Presentation (Tables)	6 Months Ended
	Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Goodwill	(In thousands of dollars) Natural Gas Construction Consolidated December 31, 2016 $ 10,095 $ 129,888 $ 139,983 Foreign currency translation adjustment — 3,600 3,600 June 30, 2017 $ 10,095 $ 133,488 $ 143,583
Accounts Receivable for Services	Centuri’s accounts receivable for these services are presented in the table below (thousands of dollars): June 30, 2017 December 31, 2016 Centuri accounts receivable for services provided to Southwest $ 10,265 $ 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): June 30, 2017 December 31, 2016 Centuri property and equipment $ 478,247 $ 451,114 Centuri accumulated provision for depreciation and amortization (240,182 ) (228,374 ) Net cash surrender value of COLI policies 111,523 106,744 Other property 13,303 12,859 Total $ 362,891 $ 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 Six Months Ended Twelve Months Ended June 30 June 30 June 30 2017 2016 2017 2016 2017 2016 Southwest Gas Corporation - natural gas operations segment: Change in COLI policies $ 1,900 $ 2,200 $ 4,700 $ 3,100 $ 9,000 $ 1,300 Interest income 614 390 1,178 757 2,269 1,766 Equity AFUDC 633 750 1,109 1,282 2,116 3,157 Miscellaneous income and (expense) (1,095 ) (904 ) (1,324 ) (948 ) (3,637 ) (2,654 ) Southwest Gas Corporation - total other income (deductions) 2,052 2,436 5,663 4,191 9,748 3,569 Construction services segment: Interest income 1 1 1 1 1 414 Foreign transaction gain (loss) (197 ) (9 ) (198 ) (19 ) (201 ) (271 ) Miscellaneous income and (expense) 190 42 445 18 1,641 924 Centuri - total other income (deductions) (6 ) 34 248 — 1,441 1,067 Corporate and administrative 1 — 1 — 1 — Consolidated Southwest Gas Holdings, Inc. - total other income (deductions) $ 2,047 $ 2,470 $ 5,912 $ 4,191 $ 11,190 $ 4,636

Components of Net Periodic Be19

Components of Net Periodic Benefit Cost (Tables)	6 Months Ended
	Jun. 30, 2017
Text Block [Abstract]
Schedule of Net Periodic Benefit Costs	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 June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 5,848 $ 5,708 $ 11,696 $ 11,417 $ 23,112 $ 23,979 Interest cost 11,521 11,507 23,041 23,013 46,055 45,127 Expected return on plan assets (13,799 ) (14,139 ) (27,598 ) (28,279 ) (55,877 ) (57,183 ) Amortization of net actuarial loss 6,001 6,316 12,002 12,633 24,635 29,005 Net periodic benefit cost $ 9,571 $ 9,392 $ 19,141 $ 18,784 $ 37,925 $ 40,928 SERP Period Ended June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 77 $ 83 $ 155 $ 165 $ 321 $ 325 Interest cost 471 465 942 930 1,871 1,778 Amortization of net actuarial loss 360 346 720 692 1,411 1,338 Net periodic benefit cost $ 908 $ 894 $ 1,817 $ 1,787 $ 3,603 $ 3,441 PBOP Period Ended June 30, Three Months Six Months Twelve Months 2017 2016 2017 2016 2017 2016 (Thousands of dollars) Service cost $ 367 $ 375 $ 734 $ 749 $ 1,484 $ 1,569 Interest cost 808 795 1,616 1,591 3,205 3,091 Expected return on plan assets (839 ) (787 ) (1,679 ) (1,575 ) (3,253 ) (3,307 ) Amortization of prior service costs 334 334 668 668 1,335 1,336 Amortization of net actuarial loss — 104 — 208 209 380 Net periodic benefit cost $ 670 $ 821 $ 1,339 $ 1,641 $ 2,980 $ 3,069

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 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 Other Total Three months ended June 30, 2017 Revenues from external customers $ 260,162 $ 277,384 $ — $ 537,546 Intersegment revenues — 22,923 — 22,923 Total $ 260,162 $ 300,307 $ — $ 560,469 Segment net income (loss) $ 9,522 $ 8,716 $ (374 ) $ 17,864 Three months ended June 30, 2016 Revenues from external customers $ 255,648 $ 266,343 $ — $ 521,991 Intersegment revenues — 25,757 — 25,757 Total $ 255,648 $ 292,100 $ — $ 547,748 Segment net income $ 2,358 $ 6,585 $ — $ 8,943 Natural Gas Construction Other Total Six months ended June 30, 2017 Revenues from external customers $ 722,764 $ 448,223 $ — $ 1,170,987 Intersegment revenues — 44,219 — 44,219 Total $ 722,764 $ 492,442 $ — $ 1,215,206 Segment net income (loss) $ 86,460 $ 1,382 $ (670 ) $ 87,172 Six months ended June 30, 2016 Revenues from external customers $ 780,748 $ 450,304 $ — $ 1,231,052 Intersegment revenues — 47,944 — 47,944 Total $ 780,748 $ 498,248 $ — $ 1,278,996 Segment net income $ 79,941 $ 4,448 $ — $ 84,389 Natural Gas Construction Other Total Twelve months ended June 30, 2017 Revenues from external customers $ 1,263,428 $ 1,038,876 $ — $ 2,302,304 Intersegment revenues — 94,396 — 94,396 Total $ 1,263,428 $ 1,133,272 $ — $ 2,396,700 Segment net income (loss) $ 125,942 $ 29,552 $ (670 ) $ 154,824 Twelve months ended June 30, 2016 Revenues from external customers $ 1,395,629 $ 964,973 $ — $ 2,360,602 Intersegment revenues — 109,195 — 109,195 Total $ 1,395,629 $ 1,074,168 $ — $ 2,469,797 Segment net income $ 113,302 $ 32,472 $ — $ 145,774

Derivatives and Fair Value Me21

Derivatives and Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 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): June 30, 2017 December 31, 2016 Contract notional amounts 11,035 10,543
Amount of Gain or Losses Recognized in Income on Derivatives	The following table sets forth the gains and (losses) recognized on the Swaps (derivatives) for the three-, six-, and twelve-month periods ended June 30, 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 Six Months Ended Twelve Months Ended Location of Gain or (Loss) June 30 June 30 June 30 Instrument Recognized in Income on Derivative 2017 2016 2017 2016 2017 2016 Swaps Net cost of gas sold $ (1,168 ) $ 5,537 $ (6,305 ) $ 4,325 $ (5,624 ) $ (1,866 ) Swaps Net cost of gas sold 1,168 * (5,537 )* 6,305 * (4,325 )* 5,624 * 1,866 * 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: June 30, 2017 Instrument Balance Sheet Location Asset Liability Net Total Swaps Other current liabilities $ 25 $ (1,575 ) $ (1,550 ) Swaps Other deferred credits 29 (681 ) (652 ) Total $ 54 $ (2,256 ) $ (2,202 ) December 31, 2016 Instrument Balance Sheet Location Asset Liability 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 Six Months Ended Twelve Months Ended (Thousands of dollars) June 30, 2017 June 30, 2017 June 30, 2017 Paid to counterparties $ 111 $ 1,412 $ 2,512 Received from counterparties $ — $ 1,685 $ 2,411
Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets	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). June 30, 2017 Instrument Balance Sheet Location Net Total Swaps Prepaids and other current assets $ 1,550 Swaps Deferred charges and other assets 652 December 31, 2016 Balance Sheet Location Net Total Swaps Other deferred credits $ (845 ) Swaps Other current liabilities (3,532
Summary of Financial Assets and Liabilities at Fair Value	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) June 30, December 31, Assets at fair value: Prepaids and other current assets - Swaps $ — $ 3,532 Deferred charges and other assets - Swaps — 845 Liabilities at fair value: Other current liabilities - Swaps (1,550 ) — Other deferred credits - Swaps (652 ) — Net Assets (Liabilities) $ (2,202 ) $ 4,377

Long-Term Debt (Tables)

Long-Term Debt (Tables)	6 Months Ended
	Jun. 30, 2017
Debt Disclosure [Abstract]
Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt	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. Because 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. June 30, 2017 December 31, 2016 Carrying Fair Carrying Fair Amount Value Amount Value (Thousands of dollars) Southwest Gas Corporation: Debentures: Notes, 4.45%, due 2020 $ 125,000 $ 130,821 $ 125,000 $ 129,703 Notes, 6.1%, due 2041 125,000 155,466 125,000 149,734 Notes, 3.875%, due 2022 250,000 259,368 250,000 254,900 Notes, 4.875%, due 2043 250,000 268,728 250,000 266,793 Notes, 3.8%, due 2046 300,000 284,172 300,000 283,029 8% Series, due 2026 75,000 96,783 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 29,356 25,000 29,290 Medium-term notes, 7.92% series, due 2027 25,000 32,320 25,000 31,905 Medium-term notes, 6.76% series, due 2027 7,500 8,914 7,500 8,769 Unamortized discount and debt issuance costs (9,644 ) (9,931 ) 1,172,856 1,197,569 Revolving credit facility and commercial paper 92,000 92,000 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 (2,304 ) (2,489 ) 197,696 197,511 Less: current maturities — (25,000 ) Long-term debt, less current maturities - Southwest Gas Corporation $ 1,462,552 $ 1,375,080 Centuri: Centuri term loan facility $ 105,559 105,641 $ 106,700 106,819 Unamortized debt issuance costs (427 ) (516 ) 105,132 106,184 Centuri secured revolving credit facility 99,943 100,091 41,185 41,292 Centuri other debt obligations 45,307 45,589 52,635 52,840 Less: current maturities (27,236 ) (25,101 ) Long-term debt, less current maturities - Centuri $ 223,146 $ 174,903 Consolidated Southwest Gas Holdings, Inc.: Southwest Gas Corporation long-term debt $ 1,462,552 $ 1,400,080 Centuri long-term debt 250,382 200,004 Less: current maturities (27,236 ) (50,101 ) Long-term debt, less current maturities - Southwest Gas Holdings, Inc. $ 1,685,698 $ 1,549,983

Equity, Other Comprehensive I23

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2017
Detailed Activities of Equity and Redeemable Noncontrolling Interest	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 six months ended June 30, 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 DECEMBER 31, 2016 47,482 $ 49,112 $ 903,123 $ (48,008 ) $ 759,263 $ (2,217 ) $ 1,661,273 $ 22,590 Common stock issuances 101 101 7,972 8,073 Net income (loss) 87,172 (95 ) 87,077 49 Redemption value adjustments 2,315 2,315 (2,315 ) Foreign currency exchange translation adj. 820 820 29 Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax 1,190 1,190 Amounts reclassified to net income, net of tax (FSIRS) 1,036 1,036 Centuri dividend to redeemable noncontrolling interest (204 ) Dividends declared Common: $0.99 per share (47,528 ) (47,528 ) JUNE 30, 2017 47,583 $ 49,213 $ 911,095 $ (44,962 ) $ 801,222 $ (2,312 ) $ 1,714,256 $ 20,149
Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss)	Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Thousands of dollars) Three Months Ended June 30, 2017 Three Months Ended June 30, 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 6,766 (2,572 ) 4,194 Regulatory adjustment (5,735 ) 2,179 (3,556 ) (6,123 ) 2,327 (3,796 ) Pension plans other comprehensive income (loss) 960 (365 ) 595 977 (372 ) 605 FSIRS (designated hedging activities): Amounts reclassifed into net income 836 (318 ) 518 837 (318 ) 519 FSIRS other comprehensive income 836 (318 ) 518 837 (318 ) 519 Total other comprehensive income (loss) - Southwest Gas Corporation 1,796 (683 ) 1,113 1,814 (690 ) 1,124 Foreign currency translation adjustments: Translation adjustments 629 — 629 70 — 70 Foreign currency other comprehensive income (loss) 629 — 629 70 — 70 Total other comprehensive income (loss) - Southwest Gas Holdings, Inc. $ 2,425 $ (683 ) $ 1,742 $ 1,884 $ (690 ) $ 1,194 Six Months Ended June 30, 2017 Six Months Ended June 30, 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 $ 668 $ (254 ) $ 414 $ 668 $ (254 ) $ 414 Amortization of net actuarial (gain)/loss 12,722 (4,834 ) 7,888 13,533 (5,143 ) 8,390 Regulatory adjustment (11,470 ) 4,358 (7,112 ) (12,246 ) 4,654 (7,592 ) Pension plans other comprehensive income (loss) 1,920 (730 ) 1,190 1,955 (743 ) 1,212 FSIRS (designated hedging activities): Amounts reclassifed into net income 1,672 (636 ) 1,036 1,673 (635 ) 1,038 FSIRS other comprehensive income 1,672 (636 ) 1,036 1,673 (635 ) 1,038 Total other comprehensive income (loss)—Southwest Gas Corporation 3,592 (1,366 ) 2,226 3,628 (1,378 ) 2,250 Foreign currency translation adjustments: Translation adjustments 849 — 849 852 — 852 Foreign currency other comprehensive income (loss) 849 — 849 852 — 852 Total other comprehensive income (loss)—Southwest Gas Holdings, Inc. $ 4,441 $ (1,366 ) $ 3,075 $ 4,480 $ (1,378 ) $ 3,102 Twelve Months Ended June 30, 2017 Twelve Months Ended June 30, 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 (508 ) 828 Amortization of net actuarial (gain)/loss 26,255 (9,976 ) 16,279 30,723 (11,675 ) 19,048 Regulatory adjustment (4,808 ) 1,826 (2,982 ) (2,318 ) 882 (1,436 ) Pension plans other comprehensive income (loss) 12 (5 ) 7 (778 ) 296 (482 ) FSIRS (designated hedging activities): Amounts reclassifed into net income 3,344 (1,271 ) 2,073 3,345 (1,271 ) 2,074 FSIRS other comprehensive income (loss) 3,344 (1,271 ) 2,073 3,345 (1,271 ) 2,074 Total other comprehensive income (loss)—Southwest Gas Corporation 3,356 (1,276 ) 2,080 2,567 (975 ) 1,592 Foreign currency translation adjustments: Translation adjustments 158 — 158 (39 ) — (39 ) Foreign currency other comprehensive income (loss) 158 — 158 (39 ) — (39 ) Total other comprehensive income (loss)—Southwest Gas Holdings, Inc. $ 3,514 $ (1,276 ) $ 2,238 $ 2,528 $ (975 ) $ 1,553 (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.
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 After-Tax Before-Tax Tax After-Tax Before-Tax Tax 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 — — — — — — 849 — 849 849 Other comprehensive income before reclassifications — — — — — — 849 — 849 849 FSIRS amounts reclassified from AOCI (1) — — — 1,672 (636 ) 1,036 — — — 1,036 Amortization of prior service cost (2) 668 (254 ) 414 — — — — — — 414 Amortization of net actuarial loss (2) 12,722 (4,834 ) 7,888 — — — — — — 7,888 Regulatory adjustment (3) (11,470 ) 4,358 (7,112 ) — — — — — — (7,112 ) Net current period other comprehensive income (loss) 1,920 (730 ) 1,190 1,672 (636 ) 1,036 849 — 849 3,075 Less: Translation adjustment attributable to redeemable noncontrolling interest — — — — — — 29 — 29 29 Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings, Inc. 1,920 (730 ) 1,190 1,672 (636 ) 1,036 820 — 820 3,046 Ending Balance AOCI June 30, 2017 $ (55,693 ) $ 21,163 $ (34,530 ) $ (14,327 ) $ 5,444 $ (8,883 ) $ (1,549 ) $ — $ (1,549 ) $ (44,962 ) (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 (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) June 30, 2017 December 31, 2016 (Thousands of dollars) Net actuarial (loss) gain $ (418,251 ) $ (430,973 ) Prior service cost (5,035 ) (5,703 ) Less: amount recognized in regulatory assets 367,593 379,063 Recognized in AOCI $ (55,693 ) $ (57,613 )
Southwest Gas Corporation [Member]
Detailed Activities of Equity and Redeemable Noncontrolling Interest	The table below provides details of activity in equity for Southwest Gas Corporation during the six months ended June 30, 2017. Effective in January 2017, Southwest became a 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 Common Stock Additional Accumulated 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 86,460 86,460 Other comprehensive income (loss): Net actuarial gain (loss) arising during period, less amortization of unamortized ben efit plan cost, net of tax 1,190 1,190 Amounts reclassified to net income,net of tax (FSIRS) 1,036 1,036 Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations (182,773 ) (182,773 ) Stock-based compensation (a) 7,369 (392 ) 6,977 Dividends declared to Southwest Gas Holdings, Inc. (39,130 ) (39,130 ) JUNE 30, 2017 47,482 $ 49,112 $ 904,715 $ (43,413 ) $ 631,226 $ 1,541,640 (a) Stock-based compensation is based on stock awards of Southwest Gas Corporation to be issued in shares of Southwest Gas Holdings, Inc.
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 After-Tax Before-Tax Tax 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) — — — 1,672 (636 ) 1,036 1,036 Amortization of prior service cost (6) 668 (254 ) 414 — — — 414 Amortization of net actuarial loss (6) 12,722 (4,834 ) 7,888 — — — 7,888 Regulatory adjustment (7) (11,470 ) 4,358 (7,112 ) — — — (7,112 ) Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation 1,920 (730 ) 1,190 1,672 (636 ) 1,036 2,226 Ending Balance AOCI June 30, 2017 $ (55,693 ) $ 21,163 $ (34,530 ) $ (14,327 ) $ 5,444 $ (8,883 ) $ (43,413 ) (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 (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 Redeema24

Construction Services Redeemable Noncontrolling Interest (Tables)	6 Months Ended
	Jun. 30, 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 (Thousands of dollars): Balance, December 31, 2016 $ 22,590 Net income (loss) attributable to redeemable noncontrolling interest 49 Foreign currency exchange translation adjustment 29 Centuri dividend to redeemable noncontrolling interest (204 ) Adjustment to redemption value (2,315 ) Balance, June 30, 2017 $ 20,149

Reorganization Impacts - Disc25

Reorganization Impacts - Discontinued Operations Solely Related to Southwest Gas Corporation (Tables)	6 Months Ended
	Jun. 30, 2017
Restructuring and Related Activities [Abstract]
Summary of Discontinued Operations - Construction Services in Condensed Consolidated Balance Sheet and Condensed Consolidated Income Statements	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: Results of Construction Services Three Six Twelve Twelve Months Ended Months Ended Months Ended Months Ended (Thousands of dollars) June 30, 2016 June 30, 2016 June 30, 2017 June 30, 2016 Construction revenues $ 292,100 $ 498,248 $ 640,830 $ 1,074,168 Operating expenses: Construction expenses 263,926 457,308 567,115 955,332 Depreciation and amortization 15,327 29,942 25,727 58,763 Operating income 12,847 10,998 47,988 60,073 Other income (deductions) 34 — 1,193 1,067 Net interest deductions 1,660 3,151 3,512 7,086 Income before income taxes 11,221 7,847 45,669 54,054 Income tax expense (benefit) 4,480 3,334 16,550 20,414 Net income 6,741 4,513 29,119 33,640 Net income attributable to noncontrolling interests 156 65 949 1,168 Discontinued operations - construction services - net income $ 6,585 $ 4,448 $ 28,170 $ 32,472

Nature of Operations and Basi26

Nature of Operations and Basis of Presentation - Additional Information (Detail) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Non-cash construction advances - non-cash investing item	$ 1,600,000	$ 2,500,000
Accrued taxes	(6,100,000)	(12,121,000)	$ 32,361,000	$ (28,140,000)
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	$ (2,823,000)	(6,456,000)	23,024,000	(17,334,000)
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		7,800,000		22,700,000
Accounting Standards Update 2016-09 [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		4,800,000		11,600,000
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		5,800,000		18,900,000
Accounting Standards Update 2016-09 [Member] | Scenario, Previously Reported [Member] | Southwest Gas Corporation [Member]
Significant Accounting Policies [Line Items]
Accrued taxes		$ 2,800,000		$ 7,800,000
Pooled Funds and Mutual Funds [Member] | Level 2 - Significant Other Observable Inputs [Member]
Significant Accounting Policies [Line Items]
Money market fund investments	7,700,000		7,700,000		$ 5,300,000
Gas Pipe Materials and Supplies [Member]
Significant Accounting Policies [Line Items]
Gas pipe materials and operating supplies	$ 39,000,000		$ 39,000,000		$ 30,000,000

Nature of Operations and Basi27

Nature of Operations and Basis of Presentation - Schedule of Goodwill (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)
Goodwill [Line Items]
Goodwill, Beginning balance	$ 139,983
Foreign currency translation adjustment	3,600
Goodwill, Ending balance	143,583
Natural Gas Operations [Member]
Goodwill [Line Items]
Goodwill, Beginning balance	10,095
Goodwill, Ending balance	10,095
Construction Services [Member]
Goodwill [Line Items]
Goodwill, Beginning balance	129,888
Foreign currency translation adjustment	3,600
Goodwill, Ending balance	$ 133,488

Nature of Operations and Basi28

Nature of Operations and Basis of Presentation - Accounts Receivable for Services (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Centuri Construction Group Inc [Member]
Segment Reporting Information [Line Items]
Centuri accounts receivable for services provided to Southwest	$ 10,265	$ 10,585

Nature of Operations and Basi29

Nature of Operations and Basis of Presentation - Schedule of Other Property and Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Net cash surrender value of COLI policies	$ 111,523	$ 106,744
Other property	13,303	12,859
Total	362,891	342,343
Centuri Construction Group Inc [Member]
Investment [Line Items]
Centuri property and equipment	478,247	451,114
Centuri accumulated provision for depreciation and amortization	$ (240,182)	$ (228,374)

Nature of Operations and Basi30

Nature of Operations and Basis of Presentation - Other Income (Deductions) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other income (deductions)
Corporate and administrative	$ 1		$ 1		$ 1
Total other income (deductions)	2,047	$ 2,470	5,912	$ 4,191	11,190	$ 4,636
Southwest Gas Corporation [Member]
Other income (deductions)
Change in COLI policies	1,900	2,200	4,700	3,100	9,000	1,300
Interest income	614	390	1,178	757	2,269	1,766
Equity AFUDC	633	750	1,109	1,282	2,116	3,157
Miscellaneous income and (expense)	(1,095)	(904)	(1,324)	(948)	(3,637)	(2,654)
Total other income (deductions)	2,052	2,436	5,663	4,191	9,748	3,569
Centuri Construction Group Inc [Member]
Other income (deductions)
Interest income	1	1	1	1	1	414
Foreign transaction gain (loss)	(197)	(9)	(198)	(19)	(201)	(271)
Miscellaneous income and (expense)	190	42	445	$ 18	1,641	924
Total other income (deductions)	$ (6)	$ 34	$ 248		$ 1,441	$ 1,067

Components of Net Periodic Be31

Components of Net Periodic Benefit Cost - Schedule of Net Periodic Benefit Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Qualified Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,848	$ 5,708	$ 11,696	$ 11,417	$ 23,112	$ 23,979
Interest cost	11,521	11,507	23,041	23,013	46,055	45,127
Expected return on plan assets	(13,799)	(14,139)	(27,598)	(28,279)	(55,877)	(57,183)
Amortization of net actuarial loss	6,001	6,316	12,002	12,633	24,635	29,005
Net periodic benefit cost	9,571	9,392	19,141	18,784	37,925	40,928
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	77	83	155	165	321	325
Interest cost	471	465	942	930	1,871	1,778
Amortization of net actuarial loss	360	346	720	692	1,411	1,338
Net periodic benefit cost	908	894	1,817	1,787	3,603	3,441
PBOP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	367	375	734	749	1,484	1,569
Interest cost	808	795	1,616	1,591	3,205	3,091
Expected return on plan assets	(839)	(787)	(1,679)	(1,575)	(3,253)	(3,307)
Amortization of prior service costs	334	334	668	668	1,335	1,336
Amortization of net actuarial loss		104		208	209	380
Net periodic benefit cost	$ 670	$ 821	$ 1,339	$ 1,641	$ 2,980	$ 3,069

Segment Information - Additiona

Segment Information - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017Segment
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

Segment Information - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 537,546	$ 521,991	$ 1,170,987	$ 1,231,052	$ 2,302,304	$ 2,360,602
Segment net income (loss)	17,864	8,943	87,172	84,389	154,824	145,774
Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	22,923	25,757	44,219	47,944	94,396	109,195
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	560,469	547,748	1,215,206	1,278,996	2,396,700	2,469,797
Natural Gas Operations [Member]
Segment Reporting Information [Line Items]
Revenues	260,162	255,648	722,764	780,748	1,263,428	1,395,629
Segment net income (loss)	9,522	2,358	86,460	79,941	125,942	113,302
Natural Gas Operations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	260,162	255,648	722,764	780,748	1,263,428	1,395,629
Construction Services [Member]
Segment Reporting Information [Line Items]
Revenues	277,384	266,343	448,223	450,304	1,038,876	964,973
Segment net income (loss)	8,716	6,585	1,382	4,448	29,552	32,472
Construction Services [Member] | Intersegment revenues [Member]
Segment Reporting Information [Line Items]
Revenues	22,923	25,757	44,219	47,944	94,396	109,195
Construction Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	300,307	$ 292,100	492,442	$ 498,248	1,133,272	$ 1,074,168
Other [Member]
Segment Reporting Information [Line Items]
Segment net income (loss)	$ (374)		$ (670)		$ (670)

Derivatives and Fair Value Me34

Derivatives and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative [Line Items]
Gains (losses) recognized in income or other comprehensive income for derivative designated cash flow hedges	$ 518,000	$ 519,000	$ 1,036,000	$ 1,038,000	$ 2,073,000	$ 2,074,000
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			Jul. 31, 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 Me35

Derivatives and Fair Value Measurements - Notional Amounts under Swaps Contracts (Detail) - MMBTU	Jun. 30, 2017	Dec. 31, 2016
Offsetting [Abstract]
Contract notional amounts	11,035,000	10,543,000

Derivatives and Fair Value Me36

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		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ (1,168)	$ 5,537	$ (6,305)	$ 4,325	$ (5,624)	$ (1,866)
Regulatory Deferral Accounting Treatment [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain or (loss) recognized in income on derivative	$ 1,168	$ (5,537)	$ 6,305	$ (4,325)	$ 5,624	$ 1,866

Derivatives and Fair Value Me37

Derivatives and Fair Value Measurements - Fair Values of Swaps in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	$ 54	$ 4,450
Liability derivatives not designated as hedging instruments	(2,256)	(73)
Net total not designated as hedging instruments	(2,202)	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		3,551
Liability derivatives not designated as hedging instruments		(19)
Net total not designated as hedging instruments		$ 3,532
Swaps [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	25
Liability derivatives not designated as hedging instruments	(1,575)
Net total not designated as hedging instruments	(1,550)
Swaps [Member] | Other Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Asset derivatives not designated as hedging instruments	29
Liability derivatives not designated as hedging instruments	(681)
Net total not designated as hedging instruments	$ (652)

Derivatives and Fair Value Me38

Derivatives and Fair Value Measurements - Paid to and Received from Counterparties for Settlements of Matured Swaps (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Paid to counterparties	$ 111	$ 1,412	$ 2,512
Received from counterparties		$ 1,685	$ 2,411

Derivatives and Fair Value Me39

Derivatives and Fair Value Measurements - Regulatory Assets/Liabilities Offsetting Derivatives at Fair Value in Condensed Consolidated Balance Sheets (Detail) - Swaps [Member] - USD ($) $ in Thousands	Jun. 30, 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		$ (3,532)
Prepaids and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ 1,550
Deferred Charges and Other Assets [Member]
Derivatives, Fair Value [Line Items]
Net Total	$ 652

Derivatives and Fair Value Me40

Derivatives and Fair Value Measurements - Summary of Financial Assets and Liabilities at Fair Value (Detail) - Level 2 - Significant Other Observable Inputs [Member] - Swaps [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Net Assets (Liabilities)	$ (2,202)	$ 4,377
Prepaids and Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets		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	(1,550)
Other Deferred Credits [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ (652)

Common Stock - Additional Infor

Common Stock - Additional Information (Detail)	Mar. 29, 2017USD ($)shares	Jan. 31, 2017	Jun. 30, 2017shares
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			101,000
BNY Mellon Capital Markets, LLC [Member]
Common stock sold through agent	0

Long-Term Debt - Schedule of Ca

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Less: current maturities	$ (27,236)	$ (50,101)
Long-term debt, less current maturities	1,685,698	1,549,983
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(27,236)	(50,101)
Long-term debt, less current maturities	1,685,698	1,549,983
Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,462,552	1,375,080
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,462,552	1,375,080
Variable-rate bonds [Member] | 2009 Series A, due 2039 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt, fair value	50,000	50,000
Carrying Amount [Member]
Debt Instrument [Line Items]
Less: current maturities	(27,236)	(50,101)
Long-term debt, less current maturities	1,685,698	1,549,983
Long-term Debt, Current and Noncurrent Abstract
Less: current maturities	(27,236)	(50,101)
Long-term debt, less current maturities	1,685,698	1,549,983
Carrying Amount [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(2,304)	(2,489)
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,462,552	1,375,080
Long-term Debt, Current and Noncurrent Abstract
Long-term debt	1,462,552	1,400,080
Less: current maturities		(25,000)
Long-term debt, less current maturities	1,462,552	1,375,080
Carrying Amount [Member] | Centuri Construction Group Inc [Member]
Debt Instrument [Line Items]
Less: current maturities	(27,236)	(25,101)
Long-term debt, less current maturities	223,146	174,903
Unamortized debt issuance costs	(427)	(516)
Long-term Debt, Current and Noncurrent Abstract
Long-term debt	250,382	200,004
Less: current maturities	(27,236)	(25,101)
Long-term debt, less current maturities	223,146	174,903
Centuri term loan/secured revolving credit facility	105,132	106,184
Carrying Amount [Member] | Centuri Secured Revolving Credit Facility [Member] | Centuri Construction Group Inc [Member]
Long-term Debt, Current and Noncurrent Abstract
Centuri term loan/secured revolving credit facility	99,943	41,185
Carrying Amount [Member] | IDRBs [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt	197,696	197,511
Carrying Amount [Member] | Centuri Term Loan Facility [Member] | Centuri Construction Group Inc [Member]
Long-term Debt, Current and Noncurrent Abstract
Centuri term loan/secured revolving credit facility	105,559	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	45,307	52,635
Carrying Amount [Member] | Debentures [Member]
Debt Instrument [Line Items]
Notes payable	1,172,856	1,197,569
Carrying Amount [Member] | Debentures [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(9,644)	(9,931)
Carrying Amount [Member] | Debentures [Member] | Notes, 4.45%, due 2020 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	125,000	125,000
Carrying Amount [Member] | Debentures [Member] | Notes, 6.1%, due 2041 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	125,000	125,000
Carrying Amount [Member] | Debentures [Member] | Notes, 3.875%, due 2022 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	250,000	250,000
Carrying Amount [Member] | Debentures [Member] | Notes, 4.875%, due 2043 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	250,000	250,000
Carrying Amount [Member] | Debentures [Member] | Notes, 3.8%, due 2046 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	300,000	300,000
Carrying Amount [Member] | Debentures [Member] | 8% Series, due 2026 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	75,000	75,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.59% series, due 2017 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable		25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.78% series, due 2022 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	25,000	25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 7.92% series, due 2027 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	25,000	25,000
Carrying Amount [Member] | Debentures [Member] | Medium-term notes, 6.76% series, due 2027 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Notes payable	7,500	7,500
Carrying Amount [Member] | Debentures [Member] | Revolving Credit Facility and Commercial Paper [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Line of credit facility	92,000	5,000
Carrying Amount [Member] | Variable-rate bonds [Member] | Tax-exempt Series A, due 2028 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2003 Series A, due 2038 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2008 Series A, due 2038 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Carrying Amount [Member] | Variable-rate bonds [Member] | 2009 Series A, due 2039 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
Unsecured debt	50,000	50,000
Market Value [Member] | Centuri Construction Group Inc [Member]
Long-term Debt, Current and Noncurrent Abstract
Centuri term loan/secured revolving credit facility	105,641	106,819
Centuri other debt obligations	45,589	52,840
Market Value [Member] | Centuri Secured Revolving Credit Facility [Member] | Centuri Construction Group Inc [Member]
Long-term Debt, Current and Noncurrent Abstract
Centuri term loan/secured revolving credit facility	100,091	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	130,821	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	155,466	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	259,368	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	268,728	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	284,172	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	96,783	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	29,356	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	32,320	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	8,914	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	92,000	5,000
Market Value [Member] | Variable-rate bonds [Member] | Tax-exempt Series A, due 2028 [Member] | Southwest Gas Corporation [Member]
Debt Instrument [Line Items]
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]
Debt Instrument [Line Items]
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]
Debt Instrument [Line Items]
Unsecured debt, fair value	$ 50,000	$ 50,000

Long-Term Debt - Schedule of 43

Long-Term Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Parenthetical) (Detail) - Southwest Gas Corporation [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 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. 1, 2020	Dec. 1, 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. 1, 2022	Apr. 1, 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. 1, 2043	Oct. 1, 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. 1, 2026	Aug. 1, 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. 3, 2022	Feb. 3, 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. 1, 2028	Dec. 1, 2028
Variable-rate bonds [Member] | 2003 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 1, 2038	Mar. 1, 2038
Variable-rate bonds [Member] | 2008 Series A, due 2038 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Mar. 1, 2038	Mar. 1, 2038
Variable-rate bonds [Member] | Market Value [Member] | 2009 Series A, due 2039 [Member]
Debt Instrument [Line Items]
Debt instrument due date	Dec. 1, 2039	Dec. 1, 2039

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended
	Mar. 31, 2017	Jun. 30, 2017
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		$ 206,000,000
Debt secured by assets		$ 501,000,000
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. 1, 2022
Southwest Gas Credit Facility [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Borrowings outstanding under facility		$ 92,000,000
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. 1, 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 In

Short-Term Debt - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended
	Mar. 31, 2017	Jun. 30, 2017
Short-term Debt [Line Items]
Short term borrowings outstanding		$ 2,500,000
Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Credit facility maximum borrowing capacity	$ 400,000,000
Credit facility expiration date		Mar. 1, 2022
Short-term Debt [Member] | Southwest Gas Credit Facility [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] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Short term borrowings outstanding		$ 2,500,000
Minimum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Commitment fee	0.075%
Maximum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Commitment fee	0.20%
Alternative Base Rate [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin		0.00%
Alternative Base Rate [Member] | Minimum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin	0.00%
Alternative Base Rate [Member] | Maximum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin	0.50%
LIBOR [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin		1.00%
LIBOR [Member] | Minimum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin	0.75%
LIBOR [Member] | Maximum [Member] | Short-term Debt [Member] | Southwest Gas Credit Facility [Member]
Short-term Debt [Line Items]
Applicable margin	1.50%

Equity, Other Comprehensive I46

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule Of Stockholders Equity [Line Items]
Balance			$ 1,661,273
Balance			$ 22,590
Balance, shares			47,482,068
Common stock issuances			$ 8,073
Net income (loss)			87,077
Net income (loss)	$ 18,121	$ 9,099	87,126	$ 84,454	$ 155,727	$ 146,942
Redemption value adjustments			2,315
Foreign currency exchange translation adj.			820
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595	605	1,190	1,212	7	(482)
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
Dividends declared Common			(47,528)
Balance	1,714,256		1,714,256		1,714,256
Balance	$ 20,149		$ 20,149		$ 20,149
Balance, shares	47,583,119		47,583,119		47,583,119
Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			$ 1,667,880
Net income (loss)			86,460
Net income (loss)	$ 9,522	2,358	86,460	79,941	$ 125,942	113,302
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax	595	605	1,190	1,212	7	(482)
Amounts reclassified into net income	518	$ 519	1,036	$ 1,038	2,073	$ 2,074
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations			(182,773)
Stock-based compensation			6,977
Dividends declared Common			(39,130)
Balance	1,541,640		1,541,640		1,541,640
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			$ 49,112
Balance, shares			47,482,000
Common stock issuances			$ 101
Common stock issuances, Shares			101,000
Other comprehensive income (loss):
Centuri dividend to redeemable noncontrolling interest			$ 0
Balance	$ 49,213		$ 49,213		$ 49,213
Balance, shares	47,583,000		47,583,000		47,583,000
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		$ 49,112
Balance, shares	47,482,000		47,482,000		47,482,000
Additional Paid-in Capital [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			$ 903,123
Common stock issuances			7,972
Other comprehensive income (loss):
Balance	$ 911,095		911,095		$ 911,095
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			7,369
Balance	904,715		904,715		904,715
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			(48,008)
Foreign currency exchange translation adj.			820
Other comprehensive income (loss):
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax			1,190
Amounts reclassified into net income			1,036
Balance	(44,962)		(44,962)		(44,962)
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			1,190
Amounts reclassified into net income			1,036
Balance	(43,413)		(43,413)		(43,413)
Retained Earnings [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			759,263
Net income (loss)			87,172
Redemption value adjustments			2,315
Other comprehensive income (loss):
Dividends declared Common			(47,528)
Balance	801,222		801,222		801,222
Retained Earnings [Member] | Southwest Gas Corporation [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			767,061
Net income (loss)			86,460
Other comprehensive income (loss):
Distribution to Southwest Gas Holdings, Inc. investment in discontinued operations			(182,773)
Stock-based compensation			(392)
Dividends declared Common			(39,130)
Balance	631,226		631,226		631,226
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			22,590
Net income (loss) attributable to temporary equity			49
Redemption value adjustments			(2,315)
Foreign currency exchange translation adj attributable to temporary equity			29
Other comprehensive income (loss):
Centuri dividend to redeemable noncontrolling interest			(204)
Dividends declared Common			0
Balance	20,149		20,149		20,149
Non-controlling Interest [Member]
Schedule Of Stockholders Equity [Line Items]
Balance			(2,217)
Net income (loss)			(95)
Other comprehensive income (loss):
Balance	$ (2,312)		$ (2,312)		$ (2,312)

Equity, Other Comprehensive I47

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Detailed Activities of Equity and Redeemable Noncontrolling Interest (Parenthetical) (Detail) - $ / shares	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Stockholders' Equity [Abstract]
Dividends declared Common, per share	$ 0.495	$ 0.450	$ 0.990	$ 0.900	$ 1.890	$ 1.710

Equity, Other Comprehensive I48

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		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost, Before-Tax Amount	$ 334	$ 334	$ 668	$ 668	$ 1,335	$ 1,336
Translation adjustments, Before-Tax Amount	629	70	849	852	158	(39)
Translation adjustments, Tax (Expense) or Benefit	0	0	0	0
Amortization of net actuarial (gain)/loss, Before-Tax Amount	6,361	6,766	12,722	13,533	26,255	30,723
Foreign currency other comprehensive income (loss), Before-Tax Amount	629	70	849	852	158	(39)
Foreign currency other comprehensive income (loss), Tax (Expense) or Benefit	0	0	0	0	0	0
Net actuarial gain/(loss), Before-Tax Amount					(22,770)	(30,519)
Total other comprehensive income (loss), Before-Tax Amount	2,425	1,884	4,441	4,480	3,514	2,528
Total other comprehensive income (loss), Tax (Expense) or Benefit	(683)	(690)	(1,366)	(1,378)	(1,276)	(975)
Regulatory adjustment, Before-Tax Amount	(5,735)	(6,123)	(11,470)	(12,246)	(4,808)	(2,318)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	960	977	1,920	1,955	12	(778)
Amounts reclassified into net income, Before-Tax Amount	836	837	1,672	1,673	3,344	3,345
FSIRS other comprehensive income (loss), Before-Tax Amount	836	837	1,672	1,673	3,344	3,345
Net actuarial gain/(loss), Tax (Expense) or Benefit					8,652	11,597
Amortization of prior service cost, Tax (Expense) or Benefit	(127)	(127)	(254)	(254)	(507)	(508)
Amortization of net actuarial (gain)/loss, Tax (Expense) or Benefit	(2,417)	(2,572)	(4,834)	(5,143)	(9,976)	(11,675)
Regulatory adjustment, Tax (Expense) or Benefit	2,179	2,327	4,358	4,654	1,826	882
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(365)	(372)	(730)	(743)	(5)	296
Amounts reclassified into net income, Tax (Expense) or Benefit	(318)	(318)	(636)	(635)	(1,271)	(1,271)
FSIRS other comprehensive income (loss), Tax (Expense) or Benefit	(318)	(318)	(636)	(635)	(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	414	414	828	828
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, Net-of-Tax Amount	(3,556)	(3,796)	(7,112)	(7,592)	(2,982)	(1,436)
Pension plans other comprehensive income (loss), Net-of-Tax Amount	595	605	1,190	1,212	7	(482)
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
FSIRS other comprehensive income (loss), Net-of-Tax Amount	518	519	1,036	1,038	2,073	2,074
Translation adjustments, Net-of-Tax Amount	629	70	849	852	158	(39)
Foreign currency other comprehensive income (loss), Net-of-Tax Amount	629	70	849	852	158	(39)
Total other comprehensive income (loss), net of tax	1,742	1,194	3,075	3,102	2,238	1,553
Southwest Gas Corporation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service cost, Before-Tax Amount			668
Amortization of net actuarial (gain)/loss, Before-Tax Amount			12,722
Total other comprehensive income (loss), Before-Tax Amount	1,796	1,814	3,592	3,628	3,356	2,567
Total other comprehensive income (loss), Tax (Expense) or Benefit	(683)	(690)	(1,366)	(1,378)	(1,276)	(975)
Regulatory adjustment, Before-Tax Amount			(11,470)
Amounts reclassified into net income, Before-Tax Amount			1,672
Amortization of prior service cost, Tax (Expense) or Benefit			(254)
Amortization of net actuarial (gain)/loss, Tax (Expense) or Benefit			(4,834)
Regulatory adjustment, Tax (Expense) or Benefit			4,358
Amounts reclassified into net income, Tax (Expense) or Benefit			(636)
Net actuarial gain/(loss), Net-of-Tax Amount					(14,118)	(18,922)
Amortization of prior service cost, Net-of-Tax Amount	207	207	414	414	828	828
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, Net-of-Tax Amount	(3,556)	(3,796)	(7,112)	(7,592)	(2,982)	(1,436)
Pension plans other comprehensive income (loss), Net-of-Tax Amount	595	605	1,190	1,212	7	(482)
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
FSIRS other comprehensive income (loss), Net-of-Tax Amount	518	519	1,036	1,038	2,073	2,074
Total other comprehensive income (loss), net of tax	$ 1,113	$ 1,124	$ 2,226	$ 2,250	$ 2,080	$ 1,592

Equity, Other Comprehensive I49

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Related Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2017USD ($)
Equity [Abstract]
Other comprehensive income loss, effective income tax rate	38.00%
Tax expense or benefit for currency translation adjustment	$ 0

Equity, Other Comprehensive I50

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Additional Information (Detail) $ in Millions	Jun. 30, 2017USD ($)
Equity [Abstract]
Amount of FSIRS existing AOCI losses expected to reclassified income in next twelve months	$ 2.1

Equity, Other Comprehensive I51

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 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	668	$ 668	$ 1,335	$ 1,336
Amortization of net actuarial loss, Defined Benefit Plans Before-Tax	6,361	6,766	12,722	13,533	26,255	30,723
Regulatory adjustment, Defined Benefit Plans Before-Tax	(5,735)	(6,123)	(11,470)	(12,246)	(4,808)	(2,318)
Net current period other comprehensive income (loss), Defined Benefit Plans Before-Tax	960	977	1,920	1,955	12	(778)
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			1,920
Ending Balance AOCI June 30, 2017, Defined Benefit Plans Before-Tax	(55,693)		(55,693)		(55,693)
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)	(254)	(254)	(507)	(508)
Amortization of net actuarial loss, Defined Benefit Plans Tax (Expense) Benefit	(2,417)	(2,572)	(4,834)	(5,143)	(9,976)	(11,675)
Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit	2,179	2,327	4,358	4,654	1,826	882
Pension plans other comprehensive income (loss), Tax (Expense) or Benefit	(365)	(372)	(730)	(743)	(5)	296
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			(730)
Ending Balance AOCI June 30, 2017, Defined Benefit Plans Tax (Expense) Benefit	21,163		21,163		21,163
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	414	414	828	828
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, Defined Benefit Plans After-Tax			(7,112)
Net defined benefit pension plans	595	605	1,190	1,212	7	(482)
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			1,190
Ending Balance AOCI June 30, 2017, Defined Benefit Plans After-Tax	(34,530)		(34,530)		(34,530)
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	837	1,672	1,673	3,344	3,345
Net current period other comprehensive income (loss), FSIRS - Before-Tax	836	837	1,672	1,673	3,344	3,345
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			1,672
Ending Balance AOCI June 30, 2017, FSIRS - Before-Tax	(14,327)		(14,327)		(14,327)
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)	(318)	(636)	(635)	(1,271)	(1,271)
Net current period other comprehensive income (loss), FSIRS - Tax (Expense) Benefit	(318)	(318)	(636)	(635)	(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			(636)
Ending Balance AOCI June 30, 2017, FSIRS - Tax (Expense) Benefit	5,444		5,444		5,444
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	1,036	1,038	2,073	2,074
Net current period other comprehensive income (loss)	518	519	1,036	1,038	2,073	2,074
Less: Translation adjustment attributable to redeemable noncontrolling interest			0
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - After-Tax			1,036
Ending Balance AOCI June 30, 2017, FSIRS - After-Tax	(8,883)		(8,883)		(8,883)
Beginning Balance AOCI December 31, 2016, Foreign Currency Items Before-Tax			(2,369)
Translation adjustments, Foreign Currency Items Before-Tax	629	70	849	852	158	(39)
Other comprehensive income before reclassifications	629	70	849	852	158	(39)
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)			849
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency Items Before-Tax			29
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings,Inc., Foreign Currency Items Before-Tax			820
Ending Balance AOCI June 30, 2017	(1,549)		(1,549)		(1,549)
Beginning Balance AOCI December 31, 2016, Foreign Currency items - Tax (Expense) Benefit			0
Translation adjustments, Foreign Currency items - Tax (Expense) Benefit	0	0	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	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	0	0
Ending Balance AOCI June 30, 2017, Foreign Currency items - Tax (Expense) Benefit	0		0		0
Beginning Balance AOCI December 31, 2016, Foreign Currency items - After-Tax			(2,369)
Translation adjustments, Foreign Currency items - After-Tax	629	70	849	852	158	(39)
Other comprehensive income before reclassifications, Foreign Currency items - After-Tax	629	70	849	852	158	(39)
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			849
Less: Translation adjustment attributable to redeemable noncontrolling interest, Foreign Currency items - After-Tax			29
Net current period other comprehensive income (loss) attributable to Southwest Gas Holdings,Inc., Foreign Currency Items - After-Tax			820
Ending Balance AOCI June 30, 2017, Foreign Currency items - After-Tax	(1,549)		(1,549)		(1,549)
Beginning Balance AOCI December 31, 2016, AOCI			(48,008)
Translation adjustments, AOCI			849
Other comprehensive income before reclassifications, AOCI			849
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
Amortization of prior service cost, AOCI	207	207	414	414	828	828
Amortization of net actuarial loss	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, AOCI			(7,112)
Total other comprehensive income (loss), net of tax	1,742	1,194	3,075	3,102	2,238	1,553
Less: Translation adjustment attributable to redeemable noncontrolling interest, AOCI			29
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI			3,046
Ending Balance AOCI June 30, 2017, AOCI	(44,962)		(44,962)		(44,962)
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			668
Amortization of net actuarial loss, Defined Benefit Plans Before-Tax			12,722
Regulatory adjustment, Defined Benefit Plans Before-Tax			(11,470)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Before-Tax			1,920
Ending Balance AOCI June 30, 2017, Defined Benefit Plans Before-Tax	(55,693)		(55,693)		(55,693)
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			(254)
Amortization of net actuarial loss, Defined Benefit Plans Tax (Expense) Benefit			(4,834)
Regulatory adjustment, Defined Benefit Plans Tax (Expense) Benefit			4,358
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans Tax (Expense) Benefit			(730)
Ending Balance AOCI June 30, 2017, Defined Benefit Plans Tax (Expense) Benefit	21,163		21,163		21,163
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	414	414	828	828
Amortization of net actuarial (gain)/loss, Defined Benefit Plans After-Tax	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, Defined Benefit Plans After-Tax			(7,112)
Net defined benefit pension plans	595	605	1,190	1,212	7	(482)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, Defined Benefit Plans After-Tax			1,190
Ending Balance AOCI June 30, 2017, Defined Benefit Plans After-Tax	(34,530)		(34,530)		(34,530)
Beginning Balance AOCI December 31, 2016, FSIRS - Before-Tax			(15,999)
FSIRS amounts reclassified from AOCI, FSIRS - Before-Tax			1,672
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Before-Tax			1,672
Ending Balance AOCI June 30, 2017, FSIRS - Before-Tax	(14,327)		(14,327)		(14,327)
Beginning Balance AOCI December 31, 2016, FSIRS - Tax (Expense) Benefit			6,080
FSIRS amounts reclassified from AOCI, FSIRS - Tax (Expense) Benefit			(636)
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - Tax (Expense) Benefit			(636)
Ending Balance AOCI June 30, 2017, FSIRS - Tax (Expense) Benefit	5,444		5,444		5,444
Beginning Balance AOCI December 31, 2016, FSIRS - After-Tax			(9,919)
FSIRS amounts reclassified from AOCI, FSIRS - After-Tax	518	519	1,036	1,038	2,073	2,074
Net current period other comprehensive income (loss)	518	519	1,036	1,038	2,073	2,074
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, FSIRS - After-Tax			1,036
Ending Balance AOCI June 30, 2017, FSIRS - After-Tax	(8,883)		(8,883)		(8,883)
Beginning Balance AOCI December 31, 2016, AOCI			(45,639)
Amounts reclassified into net income	518	519	1,036	1,038	2,073	2,074
Amortization of prior service cost, AOCI	207	207	414	414	828	828
Amortization of net actuarial loss	3,944	4,194	7,888	8,390	16,279	19,048
Regulatory adjustment, AOCI			(7,112)
Total other comprehensive income (loss), net of tax	1,113	$ 1,124	2,226	$ 2,250	2,080	$ 1,592
Net current period other comprehensive income (loss) attributable to Southwest Gas Corporation, AOCI			2,226
Ending Balance AOCI June 30, 2017, AOCI	$ (43,413)		$ (43,413)		$ (43,413)

Equity, Other Comprehensive I52

Equity, Other Comprehensive Income, and Accumulated Other Comprehensive Income - Rollforward of Accumulated Other Comprehensive Income (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 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 I53

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	Jun. 30, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Recognized in AOCI	$ (55,693)	$ (57,613)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial (loss) gain	(418,251)	(430,973)
Prior service cost	(5,035)	(5,703)
Less: amount recognized in regulatory assets	367,593	379,063
Recognized in AOCI	$ (55,693)	$ (57,613)

Construction Services Redeema54

Construction Services Redeemable Noncontrolling Interest - Additional Information (Detail) - Principal Previous Owners [Member] - Link-Line and WS Nicholls [Member]	1 Months Ended	6 Months Ended
	Oct. 31, 2014	Jun. 30, 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 hold a 3.4% equity interest in Centuri as of June 30, 2017. The terms of the agreement subject to the 3.4% interest permit the previous owners (when eligible) to exit their investment retained by requiring (if elected) the purchase of a portion of their interest based on an eligibility timeline, with incremental amounts subject to the election each year. The redemption price of the redeemable noncontrolling interest in accordance with the terms of the agreement is at fair value. The shares subject to the election cumulate (if earlier elections are not made) such that 100% of their interest retained would be 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 Redeema55

Construction Services Redeemable Noncontrolling Interest - Summary of Redeemable Noncontrolling Interest (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)
Redeemable Noncontrolling Interest [Line Items]
Balance	$ 22,590
Adjustment to redemption value	2,315
Balance	20,149
Redeemable Noncontrolling Interest (Temporary Equity) [Member]
Redeemable Noncontrolling Interest [Line Items]
Balance	22,590
Net income (loss) attributable to redeemable noncontrolling interest	49
Foreign currency exchange translation adjustment	29
Centuri dividend to redeemable noncontrolling interest	(204)
Adjustment to redemption value	(2,315)
Balance	$ 20,149

Reorganization Impacts - Disc56

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, 2016USD ($)
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 - Disc57

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, 2016USD ($)
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 - Disc58

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	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Income before income taxes	$ 11,221	$ 7,847	$ 45,669	$ 54,054
Income tax expense (benefit)	4,480	3,334	16,550	20,414
Net income	6,741	4,513	29,119	33,640
Net income attributable to noncontrolling interests	156	65	949	1,168
Discontinued operations - construction services - net income	6,585	4,448	28,170	32,472
Construction Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Construction revenues	292,100	498,248	640,830	1,074,168
Operating expenses:
Construction expenses	263,926	457,308	567,115	955,332
Depreciation and amortization	15,327	29,942	25,727	58,763
Operating income	12,847	10,998	47,988	60,073
Other income (deductions)	34		1,193	1,067
Net interest deductions	1,660	3,151	3,512	7,086
Income before income taxes	11,221	7,847	45,669	54,054
Income tax expense (benefit)	4,480	3,334	16,550	20,414
Net income	6,741	4,513	29,119	33,640
Net income attributable to noncontrolling interests	156	65	949	1,168
Discontinued operations - construction services - net income	$ 6,585	$ 4,448	$ 28,170	$ 32,472