Income Taxes - Reconciliation of Tax Provision at Statutory U.S. Rate to Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax provision at statutory U.S. rate	$ 5,495	$ 2,551	$ 8,554
Increase (decrease) in tax provision resulting from:
State and local taxes, net	(1,792)	(733)	(553)
Foreign tax rate differential	(2,079)	(296)	(3,244)
Foreign undistributed earnings, net of credits	5,329	14,211	0
Nondeductible items	1,197	891	839
Federal research and development credits	(713)	(620)	(710)
Non-territorial income	(1,079)	(1,517)	(1,458)
Withholding tax	5,454	1,078	1,762
Change in deductibility of social insurance	(3)	5	8
Uncertain tax positions	(159)	1,344	165
Stock-based compensation	213	479	0
Federal tax rate change	466	686	0
Valuation allowance	8,057	149	1,598
Foreign permanent benefit	(7,077)	(451)	(2,110)
Other	933	(166)	(47)
Total provision for income taxes	$ 14,242	$ 17,611	$ 4,804