Stock-Based Compensation Expense Included in Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 2,197	$ 1,940
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	733	530
General and Administrative Expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 1,464	$ 1,410