CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Southwest Gas Corporation	Common Stock	Common Stock Southwest Gas Corporation	Additional paid-in capital	Additional paid-in capital Southwest Gas Corporation	Accumulated other comprehensive loss	Accumulated other comprehensive loss Southwest Gas Corporation	Retained Earnings	Retained Earnings Southwest Gas Corporation	Southwest Gas Holdings, Inc.	Non-controlling Interest
Beginning balance (in shares) at Dec. 31, 2018			53,026,000	47,482,000
Beginning balance at Dec. 31, 2018			$ 54,656	$ 49,112	$ 1,305,769	$ 1,065,242	$ (52,668)	$ (49,049)	$ 944,285	$ 717,155		$ (452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			365,000
Common stock issuances			$ 365		27,024
Net income									94,809	103,389
Foreign currency exchange translation adjustment							791
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							619	619
FSIRS amounts reclassified to net income, net of tax	$ 635	$ 635					635	635
Share-based compensation						918				(160)
Dividends declared									(29,285)	(22,800)
Contributions from Southwest Gas Holdings, Inc.						22,842
Ending balance (in shares) at Mar. 31, 2019			53,391,000	47,482,000
Ending balance at Mar. 31, 2019	$ 2,346,548	1,887,903	$ 55,021	$ 49,112	1,332,793	1,089,002	(50,623)	(47,795)	1,009,809	797,584	$ 2,347,000	(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.545
FSIRS amounts reclassified to net income, net of tax	$ 2,542	2,542
Ending balance (in shares) at Mar. 31, 2020	55,126,386		55,126,000	47,482,000
Ending balance at Mar. 31, 2020	$ 2,547,895	2,114,276	$ 56,756	$ 49,112	1,470,411	1,279,208	(59,073)	(53,487)	1,079,801	839,443	2,547,895	0
Beginning balance (in shares) at Dec. 31, 2019	55,007,433		55,007,000	47,482,000
Beginning balance at Dec. 31, 2019			$ 56,637	$ 49,112	1,466,937	1,229,083	(56,732)	(55,151)	1,039,072	782,108		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			119,000
Common stock issuances			$ 119		3,474
Net income									72,542	83,599
Foreign currency exchange translation adjustment							(4,005)
Net actuarial gain (loss) arising during period, less amortization of unamortized benefit plan cost, net of tax							1,028	1,028
FSIRS amounts reclassified to net income, net of tax	$ 636	636					636	636
Share-based compensation						125				(364)
Dividends declared									(31,813)	(25,900)
Contributions from Southwest Gas Holdings, Inc.						50,000
Ending balance (in shares) at Mar. 31, 2020	55,126,386		55,126,000	47,482,000
Ending balance at Mar. 31, 2020	$ 2,547,895	$ 2,114,276	$ 56,756	$ 49,112	$ 1,470,411	$ 1,279,208	$ (59,073)	$ (53,487)	$ 1,079,801	$ 839,443	$ 2,547,895	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.570