Prepaid expenses and other assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Prepaid expenses and other assets
Prepaid subscriptions, prepaid service contracts and short-term deposits	$ 876	$ 492
CARES Act employee retention credit receivable	847	0
Research and development advance payments	445	586
Prepaid insurance	158	2,019
Reimbursement receivable from the DoD		2,674
Unbilled reimbursement receivable from the DoD		1,638
Prepaid expenses and other assets	$ 2,326	$ 7,409