Derivative Accounting - Gains and Losses from Derivative Instruments (Details) - Commodity Contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Designated as Hedging Instruments
Derivative Instruments in Designated Cash Flows Hedges
Amount reclassified from accumulated other comprehensive income to earnings related to discontinued cash flow hedges	$ 0	$ 0	$ 0
Fuel and purchased power | Designated as Hedging Instruments
Derivative Instruments in Designated Cash Flows Hedges
Loss reclassified from accumulated other comprehensive income into income (effective portion realized)	0	(763)	(1,512)
Fuel and purchased power | Not Designated as Hedging Instruments
Derivative Instruments Not Designated as Cash Flows Hedges
Net Gain (Loss) Recognized in Income	$ 216,847	$ (3,178)	$ (84,953)