Restructuring Charges (Schedule of Restructuring Charges) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 16,145	$ 28,841
Costs of Contract Revenues - Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	6,759	6,859
Costs of Contract Revenues - Other [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	2,292	16,102
General and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	185	1,189
Loss on Sale of Assets—Net [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	4,572	4,691
Other Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 2,337	$ 0