Stock Option Plan - Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Number of Shares
Beginning Balance	10,665,869	6,840,719
Granted	4,697,500	9,380,438
Exercised	(26,250)	(363,109)
Cancelled	(4,928,497)	(5,192,179)
Ending Balance	10,408,622	10,665,869
Options exercisable, at end of period	3,891,598	4,410,312
Options available for future grant	15,460,088
Weighted Average Exercise Price
Beginning Balance	$ 2.87	$ 3.81
Granted	1.08	2.62
Exercised	0.80	2.86
Cancelled	3.34	3.65
Ending Balance	1.84	2.87
Options exercisable, at end of period	$ 2.46	$ 3.85
Weighted Average Contractual Term (Years)
Outstanding, at end of period	8 years 8 months 8 days
Options exercisable, at end of period	8 years 29 days	7 years 6 months 10 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 3
Options exercisable, at end of period	$ 0	$ 0