Selected Balance Sheet Information - Schedule of accrued expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Selected Balance Sheet Information
Accrued clinical consulting services	$ 669	$ 700
Accrued vendor payments	137	225
Accrued manufacturing costs	46
Other accrued expenses	2	0
Total	$ 854	$ 925