Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Net operating loss carry-forward	$ 58,520	$ 62,535
R&D credit	10,930	10,980
Accrued liabilities and other	1,004	3,942
Stock options	850	4,416
Less: valuation allowance	(66,495)	(76,079)
Net deferred tax assets	4,809	5,794
Deferred tax liabilities
Basis difference in intangibles	(4,696)	(5,356)
Basis difference in equipment	(113)	(438)
Total net deferred tax asset	$ 0	$ 0