Commitments and Contingencies - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Finance Leases
2019 (remaining 9 months)	$ 189
2020	61
2021	0
2022	0
2023	0
2024 and thereafter	0
Total minimum lease payments	250
Less: imputed interest	(8)
Lease Obligations	242	$ 300	$ 0
Operating Leases
2019 (remaining 9 months)	2,469
2020	2,816
2021	4,197
2022	4,285
2023	4,589
2024 and thereafter	18,220
Total minimum lease payments	36,576
Less: imputed interest	(9,352)
Lease Obligations	27,224		$ 0
Sublease, payments to be received	$ 700