Organizational Restructuring (Restructuring Reserve) (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Costs Incurred Year Ended December 31, 2017	$ 10,510	$ 0	$ 0	$ 0	$ 10,510	$ 0	$ 0
Reduce staffing and exit geographic region
Restructuring Reserve [Roll Forward]
Costs Incurred Year Ended December 31, 2017					10,510
Payments for restructuring					(1,340)
Foreign Exchange					14
Accrued Balance December 31, 2017	9,184				9,184
Severance pay and benefits | Reduce staffing and exit geographic region
Restructuring Reserve [Roll Forward]
Costs Incurred Year Ended December 31, 2017					10,298
Payments for restructuring					(1,340)
Foreign Exchange					14
Accrued Balance December 31, 2017	8,972				8,972
Other direct costs | Reduce staffing and exit geographic region
Restructuring Reserve [Roll Forward]
Costs Incurred Year Ended December 31, 2017					212
Payments for restructuring					0
Foreign Exchange					0
Accrued Balance December 31, 2017	$ 212				$ 212