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Prepaid Expenses and Other Current Assets - Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]    
Prepaid insurance $ 359 $ 1,157
Prepaid clinical 1,097 89
Prepaid other 50 41
Insurance receivable   110
Other current assets 11 38
Total prepaid expenses and other current assets $ 1,517 $ 1,435