Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets [Abstract]
Prepaid research and development expenses	$ 1,600	$ 4,460
Prepaid insurance	1,295	571
Payroll tax receivable	219	32
Other prepaid expenses and other assets	115	251
Total prepaid expenses and other current assets	$ 3,229	$ 5,314