Condensed Consolidated Statements of Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenues:
Gas operating revenues	$ 195,031	$ 195,573	$ 927,500	$ 982,203	$ 1,267,025	$ 1,362,655
Construction revenues	192,315	176,226	484,925	457,009	633,966	594,208
Total operating revenues	387,346	371,799	1,412,425	1,439,212	1,900,991	1,956,863
Operating expenses:
Net cost of gas sold	47,746	53,277	317,742	387,983	409,361	533,446
Operations and maintenance	95,981	90,627	288,003	278,361	379,621	368,114
Depreciation and amortization	58,744	56,718	176,247	166,418	233,251	218,269
Taxes other than income taxes	11,153	10,600	34,021	31,065	44,684	41,264
Construction expenses	167,581	154,267	422,969	419,072	545,420	537,533
Total operating expenses	381,205	365,489	1,238,982	1,282,899	1,612,337	1,698,626
Operating income	6,141	6,310	173,443	156,313	288,654	258,237
Other income and (expenses):
Net interest deductions	(15,097)	(16,410)	(46,265)	(51,821)	(62,464)	(68,802)
Other income (deductions)	2,668	1,636	8,189	4,574	8,026	5,976
Total other income and (expenses)	(12,429)	(14,774)	(38,076)	(47,247)	(54,438)	(62,826)
Income (loss) before income taxes	(6,288)	(8,464)	135,367	109,066	234,216	195,411
Income tax expense (benefit)	(3,231)	(4,050)	47,683	38,533	84,426	69,735
Net income (loss)	(3,057)	(4,414)	87,684	70,533	149,790	125,676
Net income (loss) attributable to noncontrolling interest	(193)	(109)	(333)	(405)	(620)	(586)
Net income (loss) attributable to Southwest Gas Corporation	$ (2,864)	$ (4,305)	$ 88,017	$ 70,938	$ 150,410	$ 126,262
Basic earnings (loss) per share	$ (0.06)	$ (0.09)	$ 1.90	$ 1.54	$ 3.25	$ 2.74
Diluted earnings (loss) per share	$ (0.06)	$ (0.09)	$ 1.88	$ 1.52	$ 3.22	$ 2.72
Dividends declared per share	$ 0.330	$ 0.295	$ 0.990	$ 0.885	$ 1.285	$ 1.150
Average number of common shares outstanding	46,337	46,134	46,306	46,106	46,265	46,059
Average shares outstanding (assuming dilution)			46,732	46,534	46,704	46,493