Summary of Stock-Based Compensation Recognized (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation		$ 1,068	$ 801	$ 2,707	$ 2,533
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation		493	284	1,151	805
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	[1]	$ 575	$ 517	$ 1,556	$ 1,728

[1] Included in general and administrative stock-based compensation for the three and nine months ended September 30, 2020 is expense related to 12,295 shares and 36,160 shares of common stock, respectively, issued to certain board members in lieu of their cash compensation.