Derivative Instruments and Hedging Activities (Details) MWh in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024 USD ($) MWh	Mar. 31, 2024 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2024 USD ($) MWh	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Other Comprehensive Income (Loss), Net of Tax	$ (434,000)	$ 7,386,000	$ 9,732,000	$ (7,174,000)	$ 6,952,000	$ 2,558,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	0		8,374,000		6,626,000	(158,000)
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net	400,000,000				400,000,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	1,737				1,737
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	(434,000)		1,358,000		326,000	2,716,000
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			8,374,000			(158,000)
Regulatory assets	123,426,000				$ 123,426,000		$ 89,419,000
Proceeds from Hedge, Financing Activities	$ 23,100,000
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax		$ 36,680,000		$ 15,095,000			29,294,000	$ 22,269,000
FTR [Member] | Not Designated as Hedging Instrument [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights | MWh	9,399				9,399
Sale of Units Derivative Instruments Financial Transmission Rights | MWh	0				0
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net	$ 9,399,000				$ 9,399,000
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative, Notional Amount, Purchase (Sales), Net	400,000,000.0				400,000,000.0
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	36,246,000		$ 24,827,000		36,246,000	$ 24,827,000
Other Current Assets [Member] | FTR [Member] | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset	0				0		1,388,000
Other Current Assets [Member] | interest rate hedge | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset	$ 3,968,000				$ 3,968,000		$ 14,294,000