Significant agreements - Material Transfer Agreement (Details) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant agreements.
Collaboration revenues		$ 11,697,000	$ 10,390,000	$ 13,801,000
Material transfer agreement
Significant agreements.
Upfront cash payment	$ 1,000,000.0
Threshold period for receipt of revenue after receipt of the materials and related data package	30 days
Collaboration revenues		$ 0	$ 0	$ 1,000,000