Commitments and Contingencies (Investment Arrangements) (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Cash	$ 71,663	$ 71,427
Proportionately Consolidated Non-Controlled Joint Venture [Member]
Other Commitments [Line Items]
Cash	$ 9,100	$ 13,100
Proportionately Consolidated Non-Controlled Joint Venture [Member] | Joint Ventures That Provide Electrical Transmission Infrastructure Services [Member] | Minimum [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	85.00%
Proportionately Consolidated Non-Controlled Joint Venture [Member] | Joint Ventures That Provide Electrical Transmission Infrastructure Services [Member] | Maximum [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	90.00%