Commitments and Contingencies - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Finance Leases
2019 (remaining 6 months)	$ 126
2020	61
2021	0
2022	0
2023	0
2024 and thereafter	0
Total minimum lease payments	187
Less: imputed interest	(4)
Lease Obligations	183	$ 300	$ 0
Operating Leases
2019 (remaining 6 months)	1,648
2020	2,816
2021	4,197
2022	4,285
2023	4,589
2024 and thereafter	18,220
Total minimum lease payments	35,755
Less: imputed interest	(8,925)
Lease Obligations	26,830		$ 0
Sublease, payments to be received	$ 400