Leases - Minimum lease payments (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Minimum lease payments:
2019 (remaining three months)	$ 477
2020	1,941
2021	2,000
2022	2,059
2023	2,121
Thereafter	895
Total future minimum lease payments	9,493
Less: imputed interest	(1,991)
Present value of future minimum lease payments	7,502
Less: current portion of operating lease liability	(1,209)
Operating lease liability - noncurrent	$ 6,293