Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Other property and investments	$ 38,091	$ 37,220
Non-regulated property, equipment, and intangibles	1,750,380	1,752,094
Non-regulated accumulated provision for depreciation and amortization	(691,872)	(675,632)
Total	1,252,861	1,266,340
Southwest Gas Corporation
Property, Plant and Equipment [Line Items]
Net cash surrender value of COLI policies	150,182	146,546
Other property and investments	6,080	6,112
Total	$ 156,262	$ 152,658