Accounting for Derivative Instruments and Hedging Activities (Schedule of Derivative Assets and Liabilities) (Details) $ in Thousands, MMBTU in Millions	Dec. 31, 2022 USD ($) MMBTU	Dec. 31, 2021 USD ($) MMBTU
Derivative [Line Items]
Assets, Current	$ 587,029	$ 128,210
Assets, Long-term	94,621	26,197
Liabilities, Current	124,976	63,309
Liabilities, Long-term	18,366	40,965
Not Designated as Hedging Instrument
Derivative [Line Items]
Assets, Current	587,029	128,210
Assets, Long-term	94,621	26,197
Total derivative assets	681,650	154,407
Liabilities, Current	124,976	63,309
Liabilities, Long-term	18,366	40,965
Total derivative liabilities	$ 143,342	$ 104,274
Not Designated as Hedging Instrument | Electric Generation Fuel
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	234.9	238.0
Not Designated as Hedging Instrument | Purchased Electricity
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	5.3	8.1
Not Designated as Hedging Instrument | Natural Gas Portfolio
Derivative [Line Items]
Total derivative assets	$ 343,947	$ 79,578
Total derivative liabilities	56,222	18,850
Not Designated as Hedging Instrument | Electric Portfolio
Derivative [Line Items]
Total derivative assets	337,703	74,829
Total derivative liabilities	$ 87,120	$ 85,424
Not Designated as Hedging Instrument | Gas Derivatives
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU	322.0	347.0