Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Components of Deferred Tax Assets and Liabilities [Abstract]
Accrued liabilities	$ 2,453	$ 3,000
Allowance for doubtful accounts	23	12
Inventory valuation	424	254
Capitalized indirect inventory costs	442	383
Stock-based compensation expense	811	897
Deferred rent	520	588
Net operating loss carryforward	1,137	1,715
Basis difference on long-lived assets	608	548
Credit carryforward	747	634
Other	219	179
Total deferred income tax assets before valuation allowance	7,384	8,210
Valuation allowance	(1,247)	(914)
Total deferred income tax assets, net of valuation allowance	6,137	7,296
Prepaid advertising	(674)	(370)
Other prepaids	(762)	(610)
Basis difference of long-lived assets	(16,474)	(14,856)
Other	(4)	(18)
Deferred income tax liabilities	(17,914)	(15,854)
Net deferred income tax liabilities	(11,777)	$ (8,558)
Domestic Tax Authority | Loss and Other Credit Carryforward
Components of Deferred Tax Assets and Liabilities [Abstract]
Valuation allowance	$ (900)