Commitments, Contingencies and Uncertainties (Narrative) (Details) - USD ($) $ in Thousands			12 Months Ended
	Mar. 16, 2016	Aug. 17, 2015	Dec. 31, 2016
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies			$ 200
Four Corners Coal Plant Participants
Loss Contingencies [Line Items]
Civil Penalty Amount		$ 1,500
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest			30,000
Litigation Settlement, Amount	$ 1,000
Environmental Mitigation Project Cost		$ 6,700
Four Corners Generating Station
Loss Contingencies [Line Items]
Public Utilities, Assessed Coal Severance Surtax Penalty and Interest			$ 1,500
Litigation Settlement, Amount	$ 47