Income Taxes - Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Deferred revenue	$ 36	$ 50
Basis difference in intangible assets	3,157	3,283
Inventory reserve	2,247	2,235
Net operating loss carryforwards	6,438	4,067
Research and development tax credits	1,042	794
Accrued expenses	163	143
Stock-based compensation	322	362
Allowance for sales returns and doubtful accounts	107	160
Difference in property and equipment basis	(134)	(185)
Other	382	551
Total net deferred income tax asset	13,760	11,460
Less: Valuation allowance	(13,760)	(11,460)
Net deferred income tax asset (liability)