Stock Option Plan - Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Number of Shares
Beginning Balance	6,840,719	5,842,879
Granted	9,380,438	2,222,368
Exercised	(363,109)	(338,333)
Cancelled	(5,192,179)	(886,195)
Ending Balance	10,665,869	6,840,719
Options exercisable, at end of period	4,410,312	3,596,315
Options available for future grant	30,564
Weighted Average Exercise Price
Beginning Balance	$ 3.81	$ 3.21
Granted	2.62	3.39
Exercised	2.86	2.01
Cancelled	3.65	4.22
Ending Balance	2.87	3.81
Options exercisable, at end of period	$ 3.85	$ 4.17
Weighted Average Contractual Term (Years)
Outstanding, at end of period	8 years 8 months 1 day
Options exercisable, at end of period	7 years 6 months 10 days	6 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 0
Options exercisable, at end of period	$ 0	$ 598