Difference Between Provision for Income Taxes and Amounts Computed by Applying Federal Statutory Income Tax Rate to Loss before Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal statutory tax	$ (11,352)	$ (12,510)	$ (14,906)
Federal research credits	(2,159)	(1,630)	(1,857)
State research credits	(767)	(749)	(821)
Expiration of federal carryovers	4,651	9,200	5,472
Change in valuation allowance	10,482	6,738	13,059
Compensation related items	460	978	158
State taxes	(1,294)	(1,921)	(1,111)
Other	298	178	269
Provision for income taxes	$ 319	$ 284	$ 263