Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Contract research and development costs	$ 2,937	$ 3,344
Research and development tax credit receivable	863	827
Deferred offering costs	676
Grant reimbursement receivable		379
Value-added tax refund receivable	573	253
Other	288	314
Total prepaid expenses and other current assets	$ 5,337	$ 5,117