Goodwill and Intangible Assets - Amortization and Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, Gross (Excluding Goodwill)	$ 15,120	$ 17,838
Amortization expense	4,312	4,956	$ 5,526
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2018	4,082
2019	3,122
2020	2,292
2021	2,292
2022	1,505
Thereafter	1,827
Total amortization expense	15,120	17,838
Goodwill [Roll Forward]
Balance at January 1	31,343	36,747
Foreign currency translation adjustment	2,529	(5,404)
Balance at December 31	33,872	31,343	36,747
Amortization expense	(4,312)	$ (4,956)	$ (5,526)
Finite-lived Intangible Assets Acquired	133
Finite-Lived Intangible Assets, Translation Adjustments	$ 1,461