Lease obligation (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Lease expense	$ 1,700	$ 3,400
Restricted cash included in deposits and other noncurrent assets	$ 1,779	$ 1,779		$ 735
Weighted average remaining lease term	6 years 4 months 24 days	6 years 4 months 24 days
Weighted average incremental borrowing rate	8.5	8.5
Total minimum lease payments
2020 (remainder of year)	$ 2,980	$ 2,980
2021	6,138	6,138
2022	6,323	6,323
2023	6,512	6,512
2024	6,707	6,707
2025+	14,190	14,190
Total future minimum lease payments	42,850	42,850
Less: imputed interest	(10,246)	(10,246)
Total lease liability	32,604	32,604
Current lease liabilities	$ 3,421	$ 3,421		3,193
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherCurrentLiabilitiesMember	us-gaap:OtherCurrentLiabilitiesMember
Non-current lease liabilities	$ 29,183	$ 29,183		$ 30,975
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentLiabilitiesMember	us-gaap:OtherNoncurrentLiabilitiesMember
75 Sidney Street
Leasehold improvements	$ 1,300	$ 1,300
Entitled leasehold improvements	100	100
64 Sidney Street
Leasehold improvements	3,500	3,500
75 Hayden Avenue
Lease term			10 years
Entitled leasehold improvements	$ 6,100	$ 6,100
Total minimum lease payments
Total lease liability			$ 25,600