Background, Organization, and Summary of Significant Accounting Policies - Schedule of Other Property and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Other property	$ 22,833	$ 18,814
Total	825,069	784,173
Southwest Gas Corporation
Property, Plant and Equipment [Line Items]
Net cash surrender value of COLI policies	133,761	132,072
Other property	1,973	1,715
Total	135,734	133,787
Centuri
Property, Plant and Equipment [Line Items]
Centuri property, equipment, and intangibles	1,073,092	983,905
Centuri accumulated provision for depreciation and amortization	$ (406,590)	$ (352,333)