The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Accounting for Derivative Instruments and Hedging Activities (Schedule of Amounts Recognized in Statement of Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	$ 13,785	$ (26,807)	$ (3,574)
Credit Rating
Derivative Instruments, (Loss) Gain [Line Items]
Posted Collateral	12,800
Natural Gas Portfolio
Derivative Instruments, (Loss) Gain [Line Items]
Posted Collateral	24,000
Natural Gas Portfolio \| Credit Rating
Derivative Instruments, (Loss) Gain [Line Items]
Posted Collateral	0
Not Designated as Hedging Instrument
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	87,245	(36,519)	55,940
Not Designated as Hedging Instrument \| Energy Related Derivative \| Unrealized (Gain) Loss on Derivative Instruments, Net
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	26,686	5,534	16,970
Not Designated as Hedging Instrument \| Commodity Contract [Member] \| Electric Generation Fuel
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	76,504	5,246	10,828
Not Designated as Hedging Instrument \| Commodity Contract [Member] \| Purchased Electricity
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	(3,044)	(14,958)	48,686
Not Designated as Hedging Instrument \| Electric \| Unrealized (Gain) Loss on Derivative Instruments, Net
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments, net	$ (12,901)	$ (32,341)	$ (20,544)