v3.26.1
Derivative Instruments Gains (Loss) on Derivatives Recognized in Income (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Financial Swaps | Operating revenues    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] $ 871 $ 46
Financial Swaps | Purchased power    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] (2,564) (1,030)
Financial Swaps | Fuel expense    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] (26,512) (12,200)
Forward contracts | Operating revenues    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] 35 366
Forward contracts | Purchased power    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] (35) (444)
Forward contracts | Fuel expense    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Gain (Loss) on Derivative, Net [1] $ (339) $ (603)
[1] Excludes unrealized gains or losses on derivatives, which are recorded on the balance sheet as regulatory assets or regulatory liabilities.