v3.26.1
Debt - Schedule of Carrying Amounts and Estimated Fair Values of Long-Term Debt (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Debt Instrument [Line Items]    
Less: current maturities $ 100,000 $ 75,000
Southwest Gas Holdings, Inc. and Southwest Gas Corporation total long-term debt, less current maturities $ 3,409,859 3,433,012
Debentures: | 8% Series, due August 2026    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 8.00%  
Long-term debt, gross $ 75,000  
Debentures: | Medium-term notes, 7.92% series, due June 2027    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 7.92%  
Long-term debt, gross $ 25,000  
Debentures: | Medium-term notes, 6.76% series, due September 2027    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 6.76%  
Debentures: | Notes, 5.8%, due December 2027    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 5.80%  
Debentures: | Notes, 3.7%, due April 2028    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 3.70%  
Debentures: | Notes, 5.45%, due February 2028    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 5.45%  
Debentures: | Notes, 2.2%, due June 2030    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 2.20%  
Debentures: | Notes, 4.05%, due March 2032    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 4.05%  
Debentures: | Notes, 6.1%, due February 2041    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 6.10%  
Debentures: | Notes, 4.875%, due October 2043    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 4.875%  
Debentures: | Notes, 3.8%, due September 2046    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 3.80%  
Debentures: | Notes, 4.15%, due June 2049    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 4.15%  
Debentures: | Notes, 3.18%, due August 2051    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate 3.18%  
Carrying Amount    
Debt Instrument [Line Items]    
Less: current maturities $ 100,000 75,000
Southwest Gas Holdings, Inc. and Southwest Gas Corporation total long-term debt, less current maturities 3,409,859 3,433,012
Carrying Amount | Debentures:    
Debt Instrument [Line Items]    
Unamortized discount and debt issuance costs (21,515) (23,207)
Total 3,310,985 3,309,293
Carrying Amount | Debentures: | 8% Series, due August 2026    
Debt Instrument [Line Items]    
Long-term debt, gross 75,000 75,000
Carrying Amount | Debentures: | Medium-term notes, 7.92% series, due June 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 25,000 25,000
Carrying Amount | Debentures: | Medium-term notes, 6.76% series, due September 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 7,500 7,500
Carrying Amount | Debentures: | Notes, 5.8%, due December 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Debentures: | Notes, 3.7%, due April 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Debentures: | Notes, 5.45%, due February 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Debentures: | Notes, 2.2%, due June 2030    
Debt Instrument [Line Items]    
Long-term debt, gross 450,000 450,000
Carrying Amount | Debentures: | Notes, 4.05%, due March 2032    
Debt Instrument [Line Items]    
Long-term debt, gross 600,000 600,000
Carrying Amount | Debentures: | Notes, 6.1%, due February 2041    
Debt Instrument [Line Items]    
Long-term debt, gross 125,000 125,000
Carrying Amount | Debentures: | Notes, 4.875%, due October 2043    
Debt Instrument [Line Items]    
Long-term debt, gross 250,000 250,000
Carrying Amount | Debentures: | Notes, 3.8%, due September 2046    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Debentures: | Notes, 4.15%, due June 2049    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Debentures: | Notes, 3.18%, due August 2051    
Debt Instrument [Line Items]    
Long-term debt, gross 300,000 300,000
Carrying Amount | Revolving credit facility and commercial paper    
Debt Instrument [Line Items]    
Total 0 0
Carrying Amount | Industrial development revenue bonds:    
Debt Instrument [Line Items]    
Unamortized discount and debt issuance costs (1,126) (1,281)
Total 198,874 198,719
Carrying Amount | Industrial development revenue bonds: | Tax-exempt Series A, due December 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Carrying Amount | Industrial development revenue bonds: | 2003 Series A, due March 2038    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Carrying Amount | Industrial development revenue bonds: | 2008 Series A, due March 2038    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Carrying Amount | Industrial development revenue bonds: | 2009 Series A, due December 2039    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Fair Value | Debentures: | 8% Series, due August 2026    
Debt Instrument [Line Items]    
Long-term debt, gross 75,121 76,388
Fair Value | Debentures: | Medium-term notes, 7.92% series, due June 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 25,603 26,058
Fair Value | Debentures: | Medium-term notes, 6.76% series, due September 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 7,625 7,726
Fair Value | Debentures: | Notes, 5.8%, due December 2027    
Debt Instrument [Line Items]    
Long-term debt, gross 304,470 309,090
Fair Value | Debentures: | Notes, 3.7%, due April 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 295,530 297,450
Fair Value | Debentures: | Notes, 5.45%, due February 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 303,960 307,620
Fair Value | Debentures: | Notes, 2.2%, due June 2030    
Debt Instrument [Line Items]    
Long-term debt, gross 408,555 409,365
Fair Value | Debentures: | Notes, 4.05%, due March 2032    
Debt Instrument [Line Items]    
Long-term debt, gross 573,660 579,540
Fair Value | Debentures: | Notes, 6.1%, due February 2041    
Debt Instrument [Line Items]    
Long-term debt, gross 130,538 130,762
Fair Value | Debentures: | Notes, 4.875%, due October 2043    
Debt Instrument [Line Items]    
Long-term debt, gross 219,000 219,350
Fair Value | Debentures: | Notes, 3.8%, due September 2046    
Debt Instrument [Line Items]    
Long-term debt, gross 229,710 228,180
Fair Value | Debentures: | Notes, 4.15%, due June 2049    
Debt Instrument [Line Items]    
Long-term debt, gross 237,330 237,120
Fair Value | Debentures: | Notes, 3.18%, due August 2051    
Debt Instrument [Line Items]    
Long-term debt, gross 200,400 205,710
Fair Value | Industrial development revenue bonds: | Tax-exempt Series A, due December 2028    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Fair Value | Industrial development revenue bonds: | 2003 Series A, due March 2038    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Fair Value | Industrial development revenue bonds: | 2008 Series A, due March 2038    
Debt Instrument [Line Items]    
Long-term debt, gross 50,000 50,000
Fair Value | Industrial development revenue bonds: | 2009 Series A, due December 2039    
Debt Instrument [Line Items]    
Long-term debt, gross $ 50,000 $ 50,000