U.S. Department of Defense (DoD) expense reimbursement contract (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Unusual or Infrequent Item, or Both [Line Items]
Prepaid expenses and other current assets	$ 4,831,000		$ 3,128,000
Other Transaction Authority for Prototype Agreement
Unusual or Infrequent Item, or Both [Line Items]
Grants Receivable	13,300,000
Contra-research and development expense	4,000,000.0	$ 0
Prepaid expenses and other current assets	2,600,000
Deferred research obligation liability	$ 700,000