Income Taxes - Deferred Income Tax (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Net operating loss carryforwards	$ 121,346	$ 101,967
Research and development tax credits	6,949	5,872
Reserves and accruals	4,984	5,720
Operating lease liability	2,588	3,088
Other	4,702	3,422
Total deferred tax assets	140,569	120,069
Less: Valuation allowance	(138,214)	(117,229)
Net deferred tax assets	2,355	2,840
Deferred tax liabilities
Right-of-use assets	(2,355)	(2,840)
Total deferred tax liabilities	(2,355)	(2,840)
Net deferred tax assets	$ 0	$ 0