Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 26, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Less: current maturities	$ (41,485)			$ (297,324)
Long-term debt, less current maturities	5,865,591			4,115,684
Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	0			(275,000)
Long-term debt, less current maturities	$ 3,042,082			$ 2,440,603
MountainWest unsecured senior notes, 3.53%, due in 2028
Debt Instrument [Line Items]
Debt instrument interest rate	3.53%
MountainWest unsecured senior notes, 4.875%, due in 2041
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%
MountainWest unsecured senior notes, 3.91%, due in 2038
Debt Instrument [Line Items]
Debt instrument interest rate	3.91%
Debentures | Notes, 6.1%, due 2041 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.10%
Debentures | Notes, 4.05%, due 2032 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.05%		4.05%
Debentures | Notes, 3.875%, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate				3.875%
Debentures | Notes, 4.875%, due 2043 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.875%
Debentures | Notes, 3.8%, due 2046 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.80%
Debentures | Notes, 3.7%, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.70%
Debentures | Notes, 4.15%, due 2049 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	4.15%
Debentures | Notes, 2.2%, due 2030 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	2.20%
Debentures | Notes, 3.18%, due 2051 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	3.18%
Debentures | 8% Series, due 2026 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	8.00%
Debentures | Medium-term notes, 7.78% series, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate				7.78%
Debentures | Medium-term notes, 7.92% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	7.92%
Debentures | Medium-term notes, 6.76% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Debt instrument interest rate	6.76%
Loans Payable | SWH Term Loan Facility
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,150,000
Secured Debt | Centuri Secured Term Loan Facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,009,000
Carrying Amount
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(25,234)			$ (24,466)
Less: current maturities	(41,485)			(22,324)
Long-term debt, less current maturities	5,865,591			4,115,684
Carrying Amount | Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	0			(275,000)
Long-term debt, less current maturities	3,042,082			2,440,603
Carrying Amount | Centuri | Centuri secured revolving credit facility
Debt Instrument [Line Items]
Long-term debt, gross	150,571			103,329
Carrying Amount | Debentures | Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(26,701)			(19,959)
Long-term debt	2,705,799			2,387,541
Carrying Amount | Debentures | Notes, 6.1%, due 2041 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	125,000			125,000
Carrying Amount | Debentures | Notes, 4.05%, due 2032 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	600,000			0
Carrying Amount | Debentures | Notes, 3.875%, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	0			250,000
Carrying Amount | Debentures | Notes, 4.875%, due 2043 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	250,000			250,000
Carrying Amount | Debentures | Notes, 3.8%, due 2046 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	300,000			300,000
Carrying Amount | Debentures | Notes, 3.7%, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	300,000			300,000
Carrying Amount | Debentures | Notes, 4.15%, due 2049 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	300,000			300,000
Carrying Amount | Debentures | Notes, 2.2%, due 2030 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	450,000			450,000
Carrying Amount | Debentures | Notes, 3.18%, due 2051 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	300,000			300,000
Carrying Amount | Debentures | 8% Series, due 2026 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	75,000			75,000
Carrying Amount | Debentures | Medium-term notes, 7.78% series, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	0			25,000
Carrying Amount | Debentures | Medium-term notes, 7.92% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	25,000			25,000
Carrying Amount | Debentures | Medium-term notes, 6.76% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	7,500			7,500
Carrying Amount | Revolving credit facility and commercial paper | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt	138,000			130,000
Carrying Amount | Industrial development revenue bonds | Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(1,717)			(1,938)
Long-term debt	198,283			198,062
Carrying Amount | Industrial development revenue bonds | Tax-exempt Series A, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Carrying Amount | Industrial development revenue bonds | 2003 Series A, due 2038 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Carrying Amount | Industrial development revenue bonds | 2008 Series A, due 2038 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Carrying Amount | Industrial development revenue bonds | 2009 Series A, due 2039 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Carrying Amount | Loans Payable | SWH Term Loan Facility
Debt Instrument [Line Items]
Long-term debt, gross	1,147,747			0
Carrying Amount | Secured Debt | Centuri Secured Term Loan Facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	1,008,550			1,117,138
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 3.53%, due in 2028
Debt Instrument [Line Items]
Long-term debt, gross	101,843			102,078
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 4.875%, due in 2041
Debt Instrument [Line Items]
Long-term debt, gross	199,431			199,926
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 3.91%, due in 2038
Debt Instrument [Line Items]
Long-term debt, gross	147,812			147,735
Carrying Amount | Other debt obligations
Debt Instrument [Line Items]
Long-term debt, gross	134,274			51,665
Fair Value | Centuri | Centuri secured revolving credit facility
Debt Instrument [Line Items]
Long-term debt, gross	150,740			103,749
Fair Value | Debentures | Notes, 6.1%, due 2041 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	113,398			166,380
Fair Value | Debentures | Notes, 4.05%, due 2032 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	506,346			0
Fair Value | Debentures | Notes, 3.875%, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	0			250,603
Fair Value | Debentures | Notes, 4.875%, due 2043 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	202,383			307,538
Fair Value | Debentures | Notes, 3.8%, due 2046 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	203,559			329,055
Fair Value | Debentures | Notes, 3.7%, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	267,903			325,191
Fair Value | Debentures | Notes, 4.15%, due 2049 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	213,972			342,030
Fair Value | Debentures | Notes, 2.2%, due 2030 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	340,763			440,838
Fair Value | Debentures | Notes, 3.18%, due 2051 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	182,976			292,116
Fair Value | Debentures | 8% Series, due 2026 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	80,108			92,623
Fair Value | Debentures | Medium-term notes, 7.78% series, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	0			25,122
Fair Value | Debentures | Medium-term notes, 7.92% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	26,413			31,555
Fair Value | Debentures | Medium-term notes, 6.76% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	7,494			8,949
Fair Value | Revolving credit facility and commercial paper | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt	138,000			130,000
Fair Value | Industrial development revenue bonds | Tax-exempt Series A, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Fair Value | Industrial development revenue bonds | 2003 Series A, due 2038 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Fair Value | Industrial development revenue bonds | 2008 Series A, due 2038 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Fair Value | Industrial development revenue bonds | 2009 Series A, due 2039 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	50,000			50,000
Fair Value | Loans Payable | SWH Term Loan Facility
Debt Instrument [Line Items]
Long-term debt, gross	1,148,057			0
Fair Value | Secured Debt | Centuri Secured Term Loan Facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	977,033			1,117,841
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 3.53%, due in 2028
Debt Instrument [Line Items]
Long-term debt, gross	86,345			102,078
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 4.875%, due in 2041
Debt Instrument [Line Items]
Long-term debt, gross	152,581			199,926
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 3.91%, due in 2038
Debt Instrument [Line Items]
Long-term debt, gross	103,398			147,735
Fair Value | Other debt obligations
Debt Instrument [Line Items]
Long-term debt, gross	$ 122,980			$ 50,003