Employee Benefit Plan - Change in Benefit Obligation (Details) - Non-U.S. Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in benefit obligations
Benefit obligations	$ 16,690	$ 12,674
Gross service cost	1,397	783	$ 601
Interest cost	188	243	261
Employee contributions	530	458
Actuarial losses	30	2,296
Plan Amendment	(356)
Benefits (paid), net of transfers	(1,277)	752
Foreign exchange adjustment	1,106	(516)
Benefit obligations	18,308	16,690	$ 12,674
Other information
Amortization of prior service cost and unrecognized actuarial gains expected to be recognized	89
Accumulated benefit obligation	$ 7,984	$ 8,247