Derivative Instruments and Hedging Activities (Details) MWh in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) MWh	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Other Comprehensive Income (Loss), Net of Tax	$ 7,386	$ (7,174)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	6,626	(8,532)
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net	400,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	1,737
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	760	1,358
Accumulated Other Comprehensive Income (Loss), Net of Tax	36,680		$ 29,294	$ 22,269
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(8,532)
Regulatory assets	112,121		89,419
Proceeds from Hedge, Financing Activities	23,100
Regulatory assets	$ 112,121		89,419
FTR [Member] | Not Designated as Hedging Instrument [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights | MWh	1,399
Sale of Units Derivative Instruments Financial Transmission Rights | MWh	0
Derivative, Nonmonetary Notional Amount, Purchase (Sales), Net	$ 1,399
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative, Notional Amount, Purchase (Sales), Net	400,000
Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	36,680	$ 15,095
Other Current Assets [Member] | FTR [Member] | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset	0		1,388
Other Current Assets [Member] | interest rate hedge | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Gross Asset	$ 393		$ 14,294