U.S. Department of Defense (DoD) expense reimbursement contract (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	May 31, 2021	Dec. 31, 2020	Jul. 31, 2020
Unusual or Infrequent Item, or Both [Line Items]
Prepaid expenses and other current assets	$ 4,947		$ 4,947			$ 3,128
Other Transaction Authority for Prototype Agreement
Unusual or Infrequent Item, or Both [Line Items]
Grants Receivable					$ 17,600		$ 13,300
Contra-research and development expense	5,300	$ 600	13,400	$ 600
Prepaid expenses and other current assets	2,400		2,400			$ 900
Deferred research obligation liability	100		100
Grant expected to be received	$ 1,800		$ 1,800