Commitments and contingencies - Supplemental Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Lease Assets [Abstract]
Operating lease, right-of-use asset	$ 11,663	$ 6,156
Finance Lease, Right-of-Use Asset	119	150
Finance and Operating Lease, Right-of-Use Asset	11,782	6,306
Lease Liabilities, Current [Abstract]
Operating Lease, Liability, Current	1,921	990
Finance Lease, Liability, Current	107	127
Lease Liabilities, Noncurrent [Abstract]
Operating Lease, Liability, Noncurrent	9,994	5,373
Finance Lease, Liability, Noncurrent	0	22
Total	$ 12,022	$ 6,512