Significant agreements - Evaluation and Option Agreement (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues		$ 3,848	$ 3,842	$ 1,571	$ 1,129	$ 5,281	$ 614	$ 1,522	$ 6,384	$ 10,390	$ 13,801	$ 7,136
Deferred revenue	$ 35,156	35,156				$ 5,657				35,156	$ 5,657	$ 14,635
Evaluation and Option Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term, Bicycle Research Team (in months)	4 months
Non refundable payment for services during the BV Bicycle Research Term	$ 3,000
Threshold period for receipt of revenue after receipt of the materials and related data package	5 days
Term extension (in years)	2 months
Extension fees receivable	$ 2,000	2,000								2,000
Threshold period of notice required for termination of agreement	30 days
Upfront cash payment	$ 3,000
Collaboration revenues										0
Deferred revenue	3,000	3,000								3,000
Transaction price	$ 3,000	$ 3,000								$ 3,000