Commitments and Contingencies - Leases, Components of lease expense (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Commitments and Contingencies
Operating lease cost	$ 224	$ 449
Variable lease cost	87	167
Total lease cost	$ 311	$ 616
Weighted-average remaining operating lease term (years)	3 years 1 month 6 days	3 years 1 month 6 days
Weighted-average discount rate	8.50%	8.50%