Lease obligation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Lease expense	$ 1,800	$ 1,800
Restricted cash included in deposits and other noncurrent assets	$ 1,779	$ 1,779
Weighted average remaining lease term	6 years 7 months 6 days
Weighted average incremental borrowing rate	8.00%
Total minimum lease payments
2021 (remainder of year)	$ 6,016
2022	8,469
2023	8,723
2024	8,985
2025	9,644
Thereafter	19,945
Total future minimum lease payments	61,783
Less: imputed interest	(15,044)
Total lease liability	46,739
Current lease liabilities	$ 4,596		$ 4,198
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherCurrentLiabilitiesMember
Non-current lease liabilities	$ 42,143		$ 43,409
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentLiabilitiesMember
75 and 64 Sidney Street Leases
Leasehold improvements	$ 5,300
75 Hayden Avenue
Leasehold improvements	5,600
Deposits and other non-current assets
Restricted cash included in deposits and other noncurrent assets	$ 1,800