Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Stock compensation expense	$ 1,814	$ 2,624
Goodwill	2,366	2,235
Royalty accruals	443	353
Intangible assets	0	967
Bad debt allowance	360	389
Inter-company interest expense accrual	496	629
Net operating loss carryforwards	5,253	5,485
Credit carry-forwards	694	584
Inventory reserve	254	318
Depreciation	555
Other	362	399
Total deferred tax assets	12,597	13,983
Deferred tax liabilities:
Depreciation	0	(460)
Intangible assets	(386)	0
Other	(146)	(344)
Total deferred tax liabilities	(532)	(804)
Net deferred tax asset before valuation allowance	12,065	13,179
Valuation allowances for deferred tax assets	(12,065)	(13,179)	$ (7,832)	$ (2,006)
Net deferred tax asset	$ 0	$ 0