Accrued Expenses - Schedule of accrued expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Research and development contract costs	$ 10,412	$ 5,382
Compensation and related benefits	2,733	1,551
Other	638	419
Accrued expenses	$ 13,783	$ 7,352

Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant