Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Other property and investments	$ 57,170	$ 59,337
Total	1,313,291	1,316,479
Non-regulated property, equipment, and intangibles	1,645,159	1,616,392
Non-regulated accumulated provision for depreciation and amortization	(540,206)	(512,343)
Southwest Gas Corporation
Property, Plant and Equipment [Line Items]
Net cash surrender value of COLI policies	147,987	149,947
Other property and investments	3,181	3,146
Total	$ 151,168	$ 153,093