Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating revenues:
Gas operating revenues	$ 255,648	$ 286,643	$ 780,748	$ 839,758	$ 1,395,629	$ 1,463,873
Construction revenues	292,100	251,961	498,248	433,066	1,074,168	869,109
Total operating revenues	547,748	538,604	1,278,996	1,272,824	2,469,797	2,332,982
Operating expenses:
Net cost of gas sold	71,416	109,015	285,016	362,777	486,048	578,771
Operations and maintenance	98,744	99,344	199,541	194,854	397,886	378,558
Depreciation and amortization	72,559	66,955	147,919	134,422	283,608	262,372
Taxes other than income taxes	12,987	12,414	27,000	25,411	50,982	50,242
Construction expenses	263,926	225,829	457,308	400,757	955,332	777,773
Total operating expenses	519,632	513,557	1,116,784	1,118,221	2,173,856	2,047,716
Operating income	28,116	25,047	162,212	154,603	295,941	285,266
Other income and (expenses):
Net interest deductions	(18,221)	(17,717)	(35,942)	(35,694)	(72,127)	(72,939)
Other income (deductions)	2,470	162	4,191	2,434	4,636	5,066
Total other income and (expenses)	(15,751)	(17,555)	(31,751)	(33,260)	(67,491)	(67,873)
Income before income taxes	12,365	7,492	130,461	121,343	228,450	217,393
Income tax expense	3,266	2,429	46,007	44,401	81,508	79,627
Net income	9,099	5,063	84,454	76,942	146,942	137,766
Net income (loss) attributable to noncontrolling interests	156	114	65	10	1,168	118
Net income attributable to Southwest Gas Corporation	$ 8,943	$ 4,949	$ 84,389	$ 76,932	$ 145,774	$ 137,648
Basic earnings per share	$ 0.19	$ 0.11	$ 1.78	$ 1.65	$ 3.08	$ 2.95
Diluted earnings per share	0.19	0.10	1.77	1.63	3.06	2.92
Dividends declared per share	$ 0.450	$ 0.405	$ 0.900	$ 0.810	$ 1.710	$ 1.540
Average number of common shares outstanding	47,473	46,869	47,455	46,741	47,347	46,628
Average shares outstanding (assuming dilution)	47,811	47,290	47,787	47,164	47,693	47,070