Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Accounts receivable, due to allowance for doubtful accounts	$ 1,104	$ 900
Inventories	792	562
Operating loss carry-forwards	3,078	2,094
Stock-based compensation expense	1,231	1,981
Property and equipment, due to difference in depreciation	148	209
Research and development, alternative minimum tax credit carry-forwards	3,031	3,111
Foreign tax credit carry-forwards	754	0
State tax credit carry-forwards	2,277	2,228
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Warranty Reserves	822	675
Accrued expenses	432	424
Gross deferred tax assets	13,669	12,184
Less valuation allowance	(11,567)	(4,688)
Total deferred tax assets	2,102	7,496
Deferred tax liabilities:
Purchased intangible assets	(3,197)	(4,944)
Property and equipment, due to differences in depreciation	(2,003)	(2,849)
Other	(11)	(114)
Total deferred tax liabilities	(5,211)	(7,907)
Net deferred tax liability	(3,109)	(411)
Net deferred tax asset--non-current	24	4,686
Net deferred tax liability—non-current	$ (3,133)	$ (5,097)