Significant agreements - Material Transfer Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Significant agreements.
Collaboration revenues		$ 3,842	$ 614	$ 6,542	$ 8,520
Material transfer agreement
Significant agreements.
Upfront cash payment	$ 1,000
Threshold period for receipt of revenue after receipt of the materials and related data package	30 days
Collaboration revenues		$ 0	$ 0		$ 1,000