Restructuring Charges (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Accrued severance expense	$ 662	$ 1,403
Severance [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charges		3,549
Asset Retirements [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charges		32,309
Pre-contract Costs [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charges		6,441
Closeout Costs [Member]
Restructuring Cost And Reserve [Line Items]
Estimated restructuring charges		$ 4,194