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
Beginning balance at Dec. 31, 2018			$ 54,656		$ 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)			1,295,000
Common stock issuances			$ 1,295		104,606
Change in ownership of noncontrolling interest					(452)							452
Foreign currency exchange translation adjustment							1,578
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							1,238	1,238
FSIRS amounts reclassified to net income, net of tax	$ 1,271	$ 1,271					1,271	1,271
Net income									116,865	106,758
Share-based compensation						2,215				(312)
Contributions from Southwest Gas Holdings, Inc.						102,092
Dividends declared									(59,080)	(47,500)
Ending balance (in shares) at Jun. 30, 2019			54,321,000	47,482,000
Ending balance at Jun. 30, 2019	$ 2,419,363	1,948,222	$ 55,951	$ 49,112	1,409,923	1,169,549	(48,581)	(46,540)	1,002,070	776,101	$ 2,419,363	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.09
Beginning balance (in shares) at Mar. 31, 2019			53,391,000
Beginning balance at Mar. 31, 2019			$ 55,021		1,332,793	1,089,002	(50,623)	(47,795)	1,009,809	797,584		(452)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			930,000
Common stock issuances			$ 930		77,582
Change in ownership of noncontrolling interest					(452)							452
Foreign currency exchange translation adjustment							787
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							619	619
FSIRS amounts reclassified to net income, net of tax	$ 636	636					636	636
Net income									22,056	3,369
Share-based compensation						1,297				(152)
Contributions from Southwest Gas Holdings, Inc.						79,250
Dividends declared									(29,795)	(24,700)
Ending balance (in shares) at Jun. 30, 2019			54,321,000	47,482,000
Ending balance at Jun. 30, 2019	$ 2,419,363	1,948,222	$ 55,951	$ 49,112	1,409,923	1,169,549	(48,581)	(46,540)	1,002,070	776,101	2,419,363	0
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	$ 2,541	2,541
Ending balance (in shares) at Jun. 30, 2020	55,909,903		55,910,000	47,482,000
Ending balance at Jun. 30, 2020	$ 2,611,295	2,151,977	$ 57,540	$ 49,112	1,523,630	1,329,843	(55,617)	(51,825)	1,085,742	824,847	2,611,295	0
Beginning balance (in shares) at Dec. 31, 2019	55,007,433		55,007,000
Beginning balance at Dec. 31, 2019			$ 56,637		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)			903,000
Common stock issuances			$ 903		56,693
Change in ownership of noncontrolling interest					0							0
Foreign currency exchange translation adjustment							(2,211)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							2,055	2,055
FSIRS amounts reclassified to net income, net of tax	$ 1,271	1,271					1,271	1,271
Net income									110,507	95,541
Share-based compensation						1,260				(502)
Contributions from Southwest Gas Holdings, Inc.						99,500
Dividends declared									(63,837)	(52,300)
Ending balance (in shares) at Jun. 30, 2020	55,909,903		55,910,000	47,482,000
Ending balance at Jun. 30, 2020	$ 2,611,295	2,151,977	$ 57,540	$ 49,112	1,523,630	1,329,843	(55,617)	(51,825)	1,085,742	824,847	2,611,295	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.14
Beginning balance (in shares) at Mar. 31, 2020			55,126,000
Beginning balance at Mar. 31, 2020			$ 56,756		1,470,411	1,279,208	(59,073)	(53,487)	1,079,801	839,443		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			784,000
Common stock issuances			$ 784		53,219
Change in ownership of noncontrolling interest					0							0
Foreign currency exchange translation adjustment							1,794
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							1,027	1,027
FSIRS amounts reclassified to net income, net of tax	$ 635	635					635	635
Net income									37,965	11,942
Share-based compensation						1,135				(138)
Contributions from Southwest Gas Holdings, Inc.						49,500
Dividends declared									(32,024)	(26,400)
Ending balance (in shares) at Jun. 30, 2020	55,909,903		55,910,000	47,482,000
Ending balance at Jun. 30, 2020	$ 2,611,295	$ 2,151,977	$ 57,540	$ 49,112	$ 1,523,630	$ 1,329,843	$ (55,617)	$ (51,825)	$ 1,085,742	$ 824,847	$ 2,611,295	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.57