Restructuring Charges (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Restructuring Charges
Balance at the beginning of the period	$ 3,157
Balance at the end of the period	6
Consolidation of leased facilities | Restructuring Plan 2016
Restructuring Charges
Balance at the beginning of the period	3,157
Utilized - cash	(3,119)
Accrual adjustment	(58)
Currency translation	26
Balance at the end of the period	$ 6