Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Number of Shares
Beginning Balance			5,842,879
Granted	203,178	140,000	1,252,178	1,835,755
Exercised			(22,916)
Cancelled			(499,950)
Ending Balance	6,572,191		6,572,191		5,842,879
Options exercisable, at end of period	3,711,684		3,711,684		2,765,357
Options available for future grant	6,986,610		6,986,610
Weighted Average Exercise Price
Beginning Balance			$ 3.21
Granted			3.89
Exercised			1.87
Cancelled			3.84
Ending Balance	$ 3.93		3.93		$ 3.21
Options exercisable, at end of period	$ 4.10		$ 4.10		$ 4.39
Weighted Average Contractual Term (Years)
Outstanding, at end of period			7 years 9 months 25 days
Options exercisable, at end of period			6 years 11 months 15 days		6 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 978		$ 978
Options exercisable, at end of period	$ 704		$ 704		$ 3,603