Accounting for Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Electric Portfolio
Derivative [Line Items]
Posted Collateral	$ 14,827	$ 0
Credit Rating | Natural Gas Portfolio
Derivative [Line Items]
Posted Collateral	$ 1,000
External Credit Rating, Investment Grade [Member] | Electric Portfolio
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	95.00%
External Credit Rating, Non Investment Grade [Member] | Electric Portfolio
Derivative [Line Items]
Percentage of derivatives with credit risk exposure	5.00%
Credit Rating
Derivative [Line Items]
Posted Collateral	$ 14,800
Credit Rating | Electric Portfolio
Derivative [Line Items]
Posted Collateral	$ 0	$ 0