Department of Defense (DoD) expense reimbursement contract (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unusual or Infrequent Item, or Both [Line Items]
Prepaid expenses and other current assets	$ 3,128	$ 579
Other Transaction Authority for Prototype Agreement
Unusual or Infrequent Item, or Both [Line Items]
Grants Receivable	13,300
Contra-research and development expense	1,700
Prepaid expenses and other current assets	$ 900