Commitments and Contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies
Operating lease cost	$ 896	$ 900
Variable lease cost	662	390
Total lease cost	$ 1,558	$ 1,290
Weighted-average remaining operating lease term (years)	1 year 7 months 6 days	2 years 7 months 6 days
Weighted-average discount rate	8.56%	8.52%