v3.26.1
Schedule H, Line 4i – Schedule of Assets (Held at End of Year) (Details) - EBP 004 - USD ($)
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
EBP, Schedule of Asset Held for Investment [Line Items]    
Entity tax identification number 88-0085720  
Plan number 004  
Current value $ 683,562,499  
Participant loans 9,321,006 $ 9,100,000
Asset held for investment $ 692,883,505  
Maximum    
EBP, Schedule of Asset Held for Investment [Line Items]    
Participant loans, interest rate 10.50%  
Minimum    
EBP, Schedule of Asset Held for Investment [Line Items]    
Participant loans, interest rate 5.25%  
Investment, Identifier [Axis]: DFA | U.S. Small Cap Growth Portfolio Institutional Class    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value $ 22,726,186  
Investment, Identifier [Axis]: FIAM | Core Plus Commingled Pool Class F    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 23,197,709  
Investment, Identifier [Axis]: Fidelity Investments | 500 Index    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 73,986,463  
Investment, Identifier [Axis]: Fidelity Investments | Contrafund Pool Class A    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 143,657,806  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2010 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 3,035,018  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2015 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 4,574,356  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2020 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 14,432,866  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2025 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 22,124,940  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2030 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 37,062,094  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2035 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 27,356,002  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2040 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 38,257,480  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2045 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 32,163,082  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2050 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 26,830,501  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2055 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 20,094,378  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2060 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 11,476,100  
Investment, Identifier [Axis]: Fidelity Investments | Freedom 2065 Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 5,068,131  
Investment, Identifier [Axis]: Fidelity Investments | Freedom Retirement Commingled Pool Class D    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 3,225,182  
Investment, Identifier [Axis]: Fidelity Investments | Government Money Market Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 1,145  
Investment, Identifier [Axis]: Fidelity Investments | Low-Priced Stock Fund Class K    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value $ 27,954,484  
Investment, Identifier [Axis]: Southwest Gas Holdings, Inc. | Company common stock (753,876 shares)    
EBP, Schedule of Asset Held for Investment [Line Items]    
Number of shares 753,876  
Current value $ 60,325,197  
Investment, Identifier [Axis]: T. Rowe Price | Institutional Large Cap Value Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 23,605,652  
Investment, Identifier [Axis]: T. Rowe Price | Stable Value Common Trust Fund A    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 27,328,605  
Investment, Identifier [Axis]: Temporary Cash Investments | Temporary Cash Investments    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 6,449  
Investment, Identifier [Axis]: Vanguard Group, Inc. | International Growth Fund Admiral Shares    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value 25,213,962  
Investment, Identifier [Axis]: Victory Funds | Victory Integrity Small-Cap Value Fund    
EBP, Schedule of Asset Held for Investment [Line Items]    
Current value $ 9,858,711