Commitments and Contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Commitments and Contingencies
Operating lease cost	$ 232	$ 223
Variable lease cost	80	139
Total lease cost	$ 312	$ 362
Weighted-average remaining operating lease term (years)	5 years	2 years 4 months 24 days
Weighted-average discount rate	7.93%	8.56%