Income Taxes - Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax expense at statutory rate of 34%	$ 1,981	$ 4,427	$ 4,354
Tax expense (benefit), statutory rate	34.00%	34.00%	34.00%
State income taxes, net of federal benefit	$ 81	$ (50)	$ 54
Foreign tax rate difference	(2,057)	(1,939)	(3,708)
Research and development credit	(1,037)	(917)	(853)
Change in valuation allowance	678	162	(28)
Equity based compensation	33	(255)	54
Manufacturing credit	(191)	(61)	11
Permanent impact of non-deductible cost	766	412	(14)
Provision to return adjustments	777	(61)	(59)
Impact of Tax Cuts and Jobs Act of 2017	19,355	0	0
Other	(43)	(199)	182
Income tax expense (benefit)	$ 20,343	$ 1,519	$ (7)