Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 23,114	$ 16,407	$ 21,626
Research and alternative minimum tax credits	5,022	4,501	3,635
Accrued expenses and other	3,671	2,806	1,891
Inventory	3,456	4,248	2,280
Property and equipment	887	1,334	1,644
Total gross deferred tax assets	36,150	29,296	31,076
Less valuation allowance	(35,545)	(25,603)	(28,873)
Total deferred tax assets	605	3,693	2,203
Deferred tax liabilities
Intangible assets	(537)	(579)	(396)
Total deferred tax liabilities	(537)	(579)	(396)
Net deferred tax assets	$ 68	$ 3,114	$ 1,807