Supplemental Financial Information - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Disclosure of Accrued Expenses and Other Current Liabilities [Line Items]
Bonuses and other employee liabilities	$ 797
Research and development	191	$ 133
Other	119	90
Professional fees	0	200
Total accrued expenses and other current liabilities	$ 1,107	$ 423