Significant agreements - AstraZeneca Collaboration Agreement (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	May 31, 2018 USD ($) employee	Nov. 30, 2016 item	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Significant agreements.
Collaboration revenues			$ 4,333	$ 3,842	$ 7,926	$ 6,542
Deferred revenue			62,507		62,507		$ 35,156	$ 5,657
Option fee for development and exploitation rights	$ 5,000
Target 3 Material Right
Significant agreements.
Collaboration revenues				200		900
Target 4 Material Right
Significant agreements.
Deferred revenue			2,400		2,400		3,800
Target 6 Material Right
Significant agreements.
Collaboration revenues			1,100		1,400
AstraZeneca
Significant agreements.
Transaction price	5,700
Collaboration revenues			1,127	$ 213	1,404	$ 944
Deferred revenue			2,354		2,354		3,756	$ 4,913
AstraZeneca | Development milestone
Significant agreements.
Transaction price	700
AstraZeneca | Development Milestone | Development milestone
Significant agreements.
Customer option payment	29,000
AstraZeneca | Regulatory Milestone | Regulatory milestone
Significant agreements.
Customer option payment	23,000
AstraZeneca | Commercial milestone | Commercial milestone
Significant agreements.
Customer option payment	110,000
AstraZeneca | 2016 Collaboration Agreement
Significant agreements.
Biological Targets | item		2
AstraZeneca | May 2018 Option Exercise
Significant agreements.
Transaction price	$ 5,000		5,650		5,650				$ 6,300
Number of FTE | employee	2
AstraZeneca | May 2018 Option Exercise | Commercialization license per candidate
Significant agreements.
Customer option payment	$ 8,000
AstraZeneca | May 2018 Option Exercise | Target Three Research License and Related Services
Significant agreements.
Transaction price			650		650
AstraZeneca | May 2018 Option Exercise | Target 3 Material Right
Significant agreements.
Transaction price			1,504		1,504
Deferred revenue							$ 1,500
AstraZeneca | May 2018 Option Exercise | Target 4 Material Right
Significant agreements.
Transaction price			1,204		1,204
AstraZeneca | May 2018 Option Exercise | Target 5 Material Right
Significant agreements.
Transaction price			1,165		1,165
AstraZeneca | May 2018 Option Exercise | Target 6 Material Right
Significant agreements.
Transaction price			1,127		1,127
Deferred revenue			$ 1,100		$ 1,100