CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating revenues:
Gas operating revenues	$ 238,869	$ 255,917	$ 732,469	$ 786,630	$ 1,267,567	$ 1,362,729
Construction revenues	172,705	153,851	292,610	280,783	617,877	574,927
Total operating revenues	411,574	409,768	1,025,079	1,067,413	1,885,444	1,937,656
Operating expenses:
Net cost of gas sold	69,388	91,959	269,996	334,706	414,892	547,334
Operations and maintenance	94,935	91,884	192,022	187,734	374,267	366,574
Depreciation and amortization	58,570	55,537	117,503	109,700	231,225	211,892
Taxes other than income taxes	11,073	9,734	22,868	20,465	44,131	41,249
Construction expenses	148,700	145,274	255,388	264,805	532,106	517,427
Total operating expenses	382,666	394,388	857,777	917,410	1,596,621	1,684,476
Operating income	28,908	15,380	167,302	150,003	288,823	253,180
Other income and (expenses):
Net interest deductions	(15,290)	(18,252)	(31,168)	(35,411)	(63,777)	(69,699)
Other income (deductions)	1,452	(2,490)	5,521	2,938	6,994	(3,747)
Total other income and (expenses)	(13,838)	(20,742)	(25,647)	(32,473)	(56,783)	(73,446)
Income (loss) before income taxes	15,070	(5,362)	141,655	117,530	232,040	179,734
Income tax expense (benefit)	5,003	(1,474)	50,914	42,583	83,607	65,391
Net income (loss)	10,067	(3,888)	90,741	74,947	148,433	114,343
Net income (loss) attributable to noncontrolling interest	(41)	(212)	(140)	(296)	(536)	(583)
Net income (loss) attributable to Southwest Gas Corporation	$ 10,108	$ (3,676)	$ 90,881	$ 75,243	$ 148,969	$ 114,926
Basic earnings (loss) per share	$ 0.22	$ (0.08)	$ 1.96	$ 1.63	$ 3.22	$ 2.50
Diluted earnings (loss) per share	$ 0.22	$ (0.08)	$ 1.95	$ 1.62	$ 3.19	$ 2.48
Dividends declared per share	$ 0.330	$ 0.295	$ 0.660	$ 0.590	$ 1.250	$ 1.120
Average number of common shares outstanding	46,331	46,114	46,291	46,091	46,214	45,996
Average shares outstanding (assuming dilution)	46,757		46,704	46,504	46,654	46,423