Income Taxes - Components of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Stock based compensation	$ 158	$ 1,166
Federal and state net operating losses	47,442	39,879
Goodwill	154	220
Accrued compensation	14	9
ASC 842 - lease liabilities	524	712
Federal and state research and experimentation credit	9,152	8,173
Intangible asset differences	87	122
Deferred social security tax	212	0
Other	27	57
Total gross deferred tax assets	57,770	50,338
Less valuation allowance	(55,639)	(47,809)
Net deferred tax assets	2,131	2,529
Deferred tax liabilities:
Patent expenditures	(1,433)	(1,481)
ASC 842 - right of use assets	(386)	(528)
Fixed asset differences	(312)	(520)
Total gross deferred tax liabilities	(2,131)	(2,529)
Total net deferred tax assets	$ 0	$ 0