Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

	Quarter Ended
	March 31		June 30		September 30			December 31
(Thousands of dollars, except per share amounts)
2016
Operating revenues	$	731,248	$	547,748	$	539,969		$	641,525
Operating income		134,096		28,116		15,539			117,963
Net income		75,355		9,099		2,907			65,694
Net income attributable to Southwest Gas Corporation		75,446		8,943		2,472			65,180
Basic earnings per common share*		1.59		0.19		0.05			1.37
Diluted earnings per common share*		1.58		0.19		0.05			1.36
2015
Operating revenues	$	734,220	$	538,604	$	505,396		$	685,405
Operating income		129,556		25,047		16,143			117,586
Net income (loss)		71,879		5,063		(4,210	)		66,698
Net income (loss) attributable to Southwest Gas Corporation		71,983		4,949		(4,734	)		66,119
Basic earnings (loss) per common share*		1.54		0.11		(0.10	)		1.40
Diluted earnings (loss) per common share*		1.53		0.10		(0.10	)		1.38
2014
Operating revenues	$	608,396	$	453,153	$	432,475		$	627,683
Operating income		127,065		26,755		18,290			112,373
Net income		70,697		9,627		1,927			58,897
Net income attributable to Southwest Gas Corporation		70,783		9,627		1,970			58,746
Basic earnings per common share*		1.52		0.21		0.04			1.26
Diluted earnings per common share*		1.51		0.21		0.04			1.25

* The sum of quarterly earnings (loss) per average common share may not equal the annual earnings (loss) per share due to the ongoing change in the weighted-average number of common shares outstanding.