Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense		$ 983	$ 834	$ 2,009	$ 1,639
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense		394	314	763	658
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	[1]	$ 589	$ 520	$ 1,246	$ 981

[1] Included in general and administrative for the three and six months ended June 30, 2021 is stock-based compensation expense related to 13,713 shares and 23,862 shares, respectively, of common stock issued to certain board members in lieu of their cash compensation.