Accounting for Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Natural Gas Portfolio
Derivative [Line Items]
Posted Collateral	$ 24,000
Electric Portfolio
Derivative [Line Items]
Posted Collateral	$ 12,782	$ 20,903
External Credit Rating, Investment Grade [Member] | Electric Portfolio
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	98.90%
External Credit Rating, Non Investment Grade [Member] | Electric Portfolio
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	1.10%
Credit Rating
Derivative [Line Items]
Posted Collateral	$ 12,800
Credit Rating | Natural Gas Portfolio
Derivative [Line Items]
Posted Collateral	0
Credit Rating | Electric Portfolio
Derivative [Line Items]
Posted Collateral	$ 0	$ 0