Commitments and Contingencies - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) ft²	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) ft²	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Weighted average remaining lease term	5 years 1 month 2 days		5 years 1 month 2 days
Rent expense under non-cancelable operating leases	$ 172	$ 173	$ 317	$ 366
Weighted average discount rate	7.89%		7.89%
Lease payments	$ 37	180	$ 170	357
Area of sublease space (in sq ft) | ft²	3,537		3,537
Sublease income	$ 0	$ 18	$ 12	$ 35
BARDA [Member] | Refundable Agreements
Disaggregation of Revenue
Provision for refundable amounts	$ 52		$ 52		$ 38