Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operating revenues:
Gas operating revenues	$ 286,643	$ 271,479	$ 839,758	$ 757,972	$ 1,463,873	$ 1,325,657
Construction revenues	251,961	181,674	433,066	303,577	869,109	661,595
Total operating revenues	538,604	453,153	1,272,824	1,061,549	2,332,982	1,987,252
Operating expenses:
Net cost of gas sold	109,015	97,985	362,777	289,362	578,771	455,367
Operations and maintenance	99,344	97,620	194,854	200,028	378,558	392,920
Depreciation and amortization	66,955	62,186	134,422	125,077	262,372	244,391
Taxes other than income taxes	12,414	10,965	25,411	22,421	50,242	45,104
Construction expenses	225,829	157,642	400,757	270,841	777,773	588,737
Total operating expenses	513,557	426,398	1,118,221	907,729	2,047,716	1,726,519
Operating income	25,047	26,755	154,603	153,820	285,266	260,733
Other income and (expenses):
Net interest deductions	(17,717)	(17,305)	(35,694)	(34,824)	(72,939)	(67,356)
Other income (deductions)	162	2,863	2,434	4,475	5,066	11,254
Total other income and (expenses)	(17,555)	(14,442)	(33,260)	(30,349)	(67,873)	(56,102)
Income before income taxes	7,492	12,313	121,343	123,471	217,393	204,631
Income tax expense	2,429	2,686	44,401	43,147	79,627	70,175
Net income	5,063	9,627	76,942	80,324	137,766	134,456
Net income (loss) attributable to noncontrolling interests	114	0	10	(86)	118	(393)
Net income attributable to Southwest Gas Corporation	$ 4,949	$ 9,627	$ 76,932	$ 80,410	$ 137,648	$ 134,849
Basic earnings per share	$ 0.11	$ 0.21	$ 1.65	$ 1.73	$ 2.95	$ 2.91
Diluted earnings per share	0.10	0.21	1.63	1.71	2.92	2.88
Dividends declared per share	$ 0.405	$ 0.365	$ 0.810	$ 0.730	$ 1.540	$ 1.390
Average number of common shares outstanding	46,869	46,502	46,741	46,471	46,628	46,407
Average shares outstanding (assuming dilution)	47,290	46,948	47,164	46,910	47,070	46,860