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)