Significant agreements - AstraZeneca Collaboration Agreement (Details) $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 21, 2020 USD ($)	May 31, 2018 USD ($) employee	Nov. 30, 2016 item	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Significant agreements.
Customer option payment				$ 500		$ 500
Collaboration revenues				1,785	$ 1,571	3,593	$ 2,700
Deferred revenue				34,074		34,074			$ 35,156	$ 5,657
Option fee for development and exploitation rights		$ 5,000
Target 3 Material Right
Significant agreements.
Collaboration revenues					300		700
Target 4 Material Right
Significant agreements.
Deferred revenue				3,600		3,600			3,800
Target 6 Material Right
Significant agreements.
Collaboration revenues				0		300
AstraZeneca
Significant agreements.
Transaction price		5,700
Collaboration revenues				0	319	277	731
Deferred revenue				3,573		3,573			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
Genentech
Significant agreements.
Transaction price	$ 31,000			33,000		33,000		$ 33,000
Collaboration revenues				1,631	$ 1,196	3,079	$ 1,857
Deferred revenue				$ 26,867		$ 26,867			$ 27,579
Option fee for development and exploitation rights	$ 30,000