Derivative Instruments - Schedule of Amount of Gain (Loss) Recognized in Income on Derivatives (Details) - Not Designated as Hedging Instrument - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) recognized in income on derivatives	$ (3,009,000)	$ (7,130,000)	$ (3,121,000)	$ (23,478,000)
FTRs | Accumulated deferred fuel
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains (losses) associated with derivatives	(200,000)	(200,000)	(100,000)	(100,000)
FTRs | Electric operations
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) recognized in income on derivatives	972,000	483,000	5,106,000	1,991,000
FTRs | Purchased power
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) recognized in income on derivatives	(873,000)	(484,000)	(3,997,000)	(2,683,000)
Natural gas derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) recognized in income on derivatives	(3,108,000)	(7,129,000)	(4,230,000)	(22,786,000)
Natural gas derivatives | Accumulated deferred fuel
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) recognized in income on derivatives				$ 11,800,000
Unrealized gains (losses) associated with derivatives	(6,100,000)	$ 1,700,000	(10,800,000)
Realized gains (losses)	$ (1,500,000)		$ (100,000)