Commitments and Contingencies - Leases, Components of lease expense (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Commitments and Contingencies
Operating lease cost	$ 219	$ 669
Variable lease cost	91	282
Total lease cost	$ 310	$ 951
Weighted-average remaining operating lease term (years)	2 years 10 months 24 days	2 years 10 months 24 days
Weighted-average discount rate	8.50%	8.50%