Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Number of Shares
Beginning Balance			6,840,719
Granted	41,500	153,000	4,395,438	1,049,000
Exercised			(363,109)
Cancelled			(686,219)
Ending Balance	10,186,829		10,186,829		6,840,719
Options exercisable, at end of period	4,970,314		4,970,314		3,596,315
Options available for future grant	1,427,152		1,427,152
Weighted Average Exercise Price
Beginning Balance			$ 3.81
Granted			3.79
Exercised			2.86
Cancelled			3.86
Ending Balance	$ 3.83		3.83		$ 3.81
Options exercisable, at end of period	$ 4.13		$ 4.13		$ 4.17
Weighted Average Contractual Term (Years)
Outstanding, at end of period			8 years 3 months 7 days
Options exercisable, at end of period			7 years 2 months 23 days		6 years 10 months 24 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 899		$ 899
Options exercisable, at end of period	$ 771		$ 771		$ 598