Commitments and contingencies - Future minimum lease payments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020	$ 2,110
2021	2,871
2022	2,943
2023	3,017
2024	3,609
Total lease payments	14,550
Less imputed interest	(2,635)
Total	11,915
Finance Lease, Liability, Payment, Due [Abstract]
2020	89
2021	23
2022	0
2023	0
2024 and thereafter	0
Total lease payments	112
Less imputed interest	(5)
Total	107
Finance and Operating Lease, Liability, Payment, Due [Abstract]
2020	2,199
2021	2,894
2022	2,943
2023	3,017
2024 and thereafter	3,609
Total lease payments	14,662
Less imputed interest	(2,640)
Total	$ 12,022	$ 6,512