Commitments and Contingencies (Investment Arrangements) (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Cash	$ 43,095	$ 27,422	$ 68,484	$ 40,326
Proportionately Consolidated Non-Controlled Joint Venture [Member]
Other Commitments [Line Items]
Cash	$ 20,300	$ 11,800
Proportionately Consolidated Non-Controlled Joint Venture [Member] | Pacer [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	35.00%
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%