v3.26.1
Previously Issued Condensed Consolidated Financial Statements - Schedule of Effects of the Prior-Period Errors on the Condensed Consolidated Statements of Equity (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance $ 4,101,678 $ 3,961,119 $ 3,751,445 $ 3,681,422
Net income (loss) 42,122 138,374 (40,154) 113,870
Ending balance 4,125,290 4,101,678 4,088,534 3,751,445
Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance 3,662,448 3,524,966 3,380,149 3,235,486
Net income (loss) 40,757 137,771 45,646 142,595
Ending balance 3,848,887 3,662,448 3,383,619 3,380,149
Retained Earnings        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance 1,160,327 1,022,846 827,453 758,649
Net income (loss) 42,122 138,374 (40,154) 113,870
Ending balance 1,155,629 1,160,327 742,452 827,453
Retained Earnings | Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance 1,451,880 1,314,911 1,202,052 1,059,773
Net income (loss) 40,757 137,771 45,646 142,595
Ending balance $ 1,492,562 $ 1,451,880 1,203,006 1,202,052
Parent        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance     3,578,886 3,504,187
Net income (loss)     (40,154) 113,870
Ending balance     3,647,386 3,578,886
As Reported        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Net income (loss)     (12,883)  
Ending balance     4,115,805  
As Reported | Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance     3,416,872  
Net income (loss)     33,677 142,942
Ending balance     3,408,373 3,416,872
As Reported | Retained Earnings        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Ending balance     769,723  
As Reported | Retained Earnings | Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance     1,238,775  
Ending balance     1,227,760 1,238,775
As Reported | Parent        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Ending balance     3,674,657  
Adjustments        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Net income (loss)     (27,271)  
Ending balance     (27,271)  
Adjustments | Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance     (36,723)  
Net income (loss)     11,969 (347)
Ending balance     (24,754) (36,723)
Adjustments | Retained Earnings        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Ending balance     (27,271)  
Adjustments | Retained Earnings | Southwest Gas Corporation        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Beginning balance     (36,723)  
Ending balance     (24,754) $ (36,723)
Adjustments | Parent        
Increase (Decrease) in Stockholders' Equity [Roll Forward]        
Ending balance     $ (27,271)