Business Acquisitions - Schedule of Pro Forma Consolidated Financial Information (Details) - Drum Parent, Inc. - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Business acquisition, pro forma adjustment, transaction costs			$ 30,000
Business acquisition, pro forma adjustment, transaction costs, incremental interest expense of new loan facility	$ 7,000	$ 9,000	27,000	$ 24,500
Total operating revenues	956,120	907,512	2,903,658	2,702,062
Net income (loss) attributable to Southwest Gas Holdings, Inc.	$ (8,918)	$ 12,688	$ 120,828	$ 84,049
Basic earnings per share (in USD per Share)	$ (0.15)	$ 0.23	$ 2.06	$ 1.51
Diluted earnings per share (in USD per Share)	$ (0.15)	$ 0.23	$ 2.06	$ 1.51