Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax provision at statutory U.S. rate	$ 2,551	$ 8,554	$ 12,232
Increase (decrease) in tax provision resulting from:
State and local taxes, net	(733)	(553)	(554)
Foreign tax rate differential	(296)	(3,244)	(5,762)
Foreign undistributed earnings, net of credits	14,211	0	0
Nondeductible items	891	839	874
Federal research and development credits	(620)	(710)	(678)
Non-territorial income	(1,517)	(1,458)	(1,906)
Withholding tax	1,078	1,762	1,985
Change in deductibility of social insurance	5	8	649
Uncertain tax positions	1,344	165	10
Stock-based compensation	479	0	0
Federal tax rate change	686	0	0
Valuation allowance	149	1,598	621
Foreign permanent benefit	(451)	(2,110)	(675)
Other	(166)	(47)	6
Total provision for income taxes	$ 17,611	$ 4,804	$ 6,802