Commitments and Contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commitments and Contingencies
Operating lease cost	$ 273	$ 220	$ 505	$ 443
Variable lease cost	143	164	222	303
Total lease cost	$ 416	$ 384	$ 727	$ 746
Weighted-average remaining operating lease term (years)	4 years 9 months 18 days	2 years 2 months 12 days	4 years 9 months 18 days	2 years 2 months 12 days
Weighted-average discount rate	7.92%	8.59%	7.92%	8.59%