Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Less: current maturities	$ (291,069)	$ (297,324)
Long-term debt, less current maturities	4,559,758	4,115,684
Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(250,000)	(275,000)
Long-term debt, less current maturities	$ 2,903,556	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%
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%
Carrying Amount
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	$ (23,546)	(24,466)
Less: current maturities	(41,069)	(22,324)
Long-term debt, less current maturities	4,559,758	4,115,684
Carrying Amount | Southwest Gas Corporation
Debt Instrument [Line Items]
Less: current maturities	(250,000)	(275,000)
Long-term debt, less current maturities	2,903,556	2,440,603
Carrying Amount | Centuri secured revolving credit facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	108,035	103,329
Carrying Amount | Debentures | Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(27,091)	(19,959)
Long-term debt	2,955,409	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	250,000	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	0	130,000
Carrying Amount | Industrial development revenue bonds | Southwest Gas Corporation
Debt Instrument [Line Items]
Unamortized discount and debt issuance costs	(1,853)	(1,938)
Long-term debt	198,147	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 | Secured Debt | Centuri secured term loan facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	1,014,275	1,117,138
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 3.53%, due in 2028
Debt Instrument [Line Items]
Long-term debt, gross	102,001	102,078
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 4.875%, due in 2041
Debt Instrument [Line Items]
Long-term debt, gross	199,765	199,926
Carrying Amount | Unsecured Debt | MountainWest unsecured senior notes, 3.91%, due in 2038
Debt Instrument [Line Items]
Long-term debt, gross	147,760	147,735
Carrying Amount | Other debt obligations
Debt Instrument [Line Items]
Long-term debt, gross	148,981	51,665
Fair Value | Centuri secured revolving credit facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	108,060	103,749
Fair Value | Debentures | Notes, 6.1%, due 2041 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	146,293	166,380
Fair Value | Debentures | Notes, 4.05%, due 2032 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	598,242	0
Fair Value | Debentures | Notes, 3.875%, due 2022 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	249,993	250,603
Fair Value | Debentures | Notes, 4.875%, due 2043 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	272,933	307,538
Fair Value | Debentures | Notes, 3.8%, due 2046 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	276,144	329,055
Fair Value | Debentures | Notes, 3.7%, due 2028 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	303,660	325,191
Fair Value | Debentures | Notes, 4.15%, due 2049 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	296,361	342,030
Fair Value | Debentures | Notes, 2.2%, due 2030 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	398,066	440,838
Fair Value | Debentures | Notes, 3.18%, due 2051 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	246,813	292,116
Fair Value | Debentures | 8% Series, due 2026 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	86,880	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	28,987	31,555
Fair Value | Debentures | Medium-term notes, 6.76% series, due 2027 | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt, gross	8,230	8,949
Fair Value | Revolving credit facility and commercial paper | Southwest Gas Corporation
Debt Instrument [Line Items]
Long-term debt	0	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 | Secured Debt | Centuri secured term loan facility | Centuri
Debt Instrument [Line Items]
Long-term debt, gross	1,000,329	1,117,841
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 3.53%, due in 2028
Debt Instrument [Line Items]
Long-term debt, gross	95,819	102,078
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 4.875%, due in 2041
Debt Instrument [Line Items]
Long-term debt, gross	176,488	199,926
Fair Value | Unsecured Debt | MountainWest unsecured senior notes, 3.91%, due in 2038
Debt Instrument [Line Items]
Long-term debt, gross	131,379	147,735
Fair Value | Other debt obligations
Debt Instrument [Line Items]
Long-term debt, gross	$ 142,712	$ 50,003