Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Inventory reserves	$ 1,396	$ 1,228
Capitalized research costs	44	52
Capitalized inventory costs	704	926
Net operating losses	485	582
Acquired intangible assets	136	148
Accrued liabilities	4,739	5,194
Income tax credits	12,509	11,251
Stock-based compensation	3,376	2,064
Total deferred tax assets	23,389	21,445
Deferred tax liabilities:
Depreciation	(2,924)	(2,639)
Allowance for doubtful accounts	(241)	(223)
Amortization of intangible assets	(780)	(1,274)
Other	(1,479)	(2,752)
Total deferred tax liabilities	(5,424)	(6,888)
Net deferred tax assets before valuation allowance	17,965	14,557
Less: Valuation allowance	(8,635)	(6,678)
Net deferred tax assets	$ 9,330	$ 7,879