Income Taxes - Reconciliation of Provision for Income Taxes at Statutory Rate and Provision (Benefit) for Income Taxes at Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax at federal statutory rate	$ (9,811)	$ (6,659)	$ (3,846)
Increase/(decrease) in tax resulting from:
State income tax expense, net of federal tax effect	(2,749)	(421)	(183)
Nondeductible permanent items	(1,522)	1,506	1,012
Foreign rate differential	552	599	662
Tax rate change	134	7,226	(13)
Adjustment to deferred taxes	307	37	(132)
Change in valuation allowance	15,805	(2,291)	2,351
Uncertain tax positions	143	76	83
Nonqualified stock option and performance award windfall upon exercise	(1,983)
Other	(80)	(26)	42
Total	$ 796	$ 47	$ (24)