CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Southwest Gas Corporation	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value	Southwest Gas Holdings, Inc. Common Stock, $1 Par Value 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.
Beginning balance (in shares) at Dec. 31, 2019			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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,452,000
Common stock issuances			$ 1,452		92,877
Foreign currency exchange translation adjustment							(1,187)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							3,082	3,082
FSIRS amounts reclassified to net income, net of tax	$ 2,054	$ 2,054					2,054	2,054
Net income (loss)									128,780	79,568
Share-based compensation						2,397				(641)
Contributions from Southwest Gas Holdings, Inc.						131,961
Dividends declared									(96,161)	(79,300)
Redemption value adjustments									(17,573)
Ending balance (in shares) at Sep. 30, 2020			56,459,000	47,482,000
Ending balance at Sep. 30, 2020		2,144,273	$ 58,089	$ 49,112	1,559,814	1,363,441	(52,783)	(50,015)	1,054,118	781,735	$ 2,619,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.71
Beginning balance (in shares) at Jun. 30, 2020			55,910,000
Beginning balance at Jun. 30, 2020			$ 57,540		1,523,630	1,329,843	(55,617)	(51,825)	1,085,742	824,847
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			549,000
Common stock issuances			$ 549		36,184
Foreign currency exchange translation adjustment							1,024
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	$ 783	783					783	783
Net income (loss)									18,273	(15,973)
Share-based compensation						1,137				(139)
Contributions from Southwest Gas Holdings, Inc.						32,461
Dividends declared									(32,324)	(27,000)
Redemption value adjustments									(17,573)
Ending balance (in shares) at Sep. 30, 2020			56,459,000	47,482,000
Ending balance at Sep. 30, 2020		2,144,273	$ 58,089	$ 49,112	1,559,814	1,363,441	(52,783)	(50,015)	1,054,118	781,735	2,619,238
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.57
FSIRS amounts reclassified to net income, net of tax	$ 1,653	1,653
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		2,462,794	$ 62,009	$ 49,112	1,823,889	1,617,796	(55,951)	(55,759)	1,079,869	851,645	2,909,816
Beginning balance (in shares) at Dec. 31, 2020	57,192,925		57,193,000
Beginning balance at Dec. 31, 2020			$ 58,823		1,609,155	1,410,345	(61,003)	(61,135)	1,067,978	835,146
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			3,186,000
Common stock issuances			$ 3,186		214,734
Foreign currency exchange translation adjustment							(324)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							4,136	4,136
FSIRS amounts reclassified to net income, net of tax	$ 1,240	1,240					1,240	1,240
Net income (loss)									130,836	102,584
Share-based compensation						4,868				(685)
Contributions from Southwest Gas Holdings, Inc.						202,583
Dividends declared									(106,303)	(85,400)
Redemption value adjustments	$ 12,642								(12,642)
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		2,462,794	$ 62,009	$ 49,112	1,823,889	1,617,796	(55,951)	(55,759)	1,079,869	851,645	2,909,816
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 1.785
Beginning balance (in shares) at Jun. 30, 2021			59,088,000
Beginning balance at Jun. 30, 2021			$ 60,718		1,733,572	1,529,419	(55,688)	(57,552)	1,108,279	908,757
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuances (in shares)			1,291,000
Common stock issuances			$ 1,291		90,317
Foreign currency exchange translation adjustment							(2,056)
Net actuarial gain arising during period, less amortization of unamortized benefit plan cost, net of tax							1,380	1,380
FSIRS amounts reclassified to net income, net of tax	$ 413	413					413	413
Net income (loss)									(11,576)	(27,544)
Share-based compensation						1,435				(168)
Contributions from Southwest Gas Holdings, Inc.						86,942
Dividends declared									(36,098)	(29,400)
Redemption value adjustments									19,264
Ending balance (in shares) at Sep. 30, 2021	60,378,684		60,379,000	47,482,000
Ending balance at Sep. 30, 2021		$ 2,462,794	$ 62,009	$ 49,112	$ 1,823,889	$ 1,617,796	$ (55,951)	$ (55,759)	$ 1,079,869	$ 851,645	$ 2,909,816
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in USD per share)	$ 0.595