Significant agreements - AstraZeneca Collaboration Agreement (Details) $ in Thousands		1 Months Ended		3 Months Ended								12 Months Ended
	May 31, 2019 employee	May 31, 2018 USD ($)	Nov. 30, 2016 USD ($) item	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant agreements.
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				5,657				35,156	5,657	14,635
AstraZeneca
Significant agreements.
Biological Targets | item			6
Transaction price		$ 5,700
Transaction price raised			$ 2,000
Collaboration revenues												2,696	1,683	1,386
Deferred revenue				3,756				4,913				3,756	4,913	4,727
AstraZeneca | Target One
Significant agreements.
Transaction price			600
AstraZeneca | Target Two
Significant agreements.
Transaction price			600
Collaboration revenues												0
AstraZeneca | Target Three Research License and Related Services
Significant agreements.
Collaboration revenues												2,700	1,500	400
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
Transaction price			$ 1,200
Deferred revenue				0				$ 0				0	0
AstraZeneca | 2016 Collaboration Agreement | Target One and Target Two Research License and Related Services
Significant agreements.
Collaboration revenues												0	$ 200	$ 1,000
AstraZeneca | 2016 Collaboration Agreement | Commercialization license per candidate
Significant agreements.
Customer option payment			$ 8,000
AstraZeneca | May 2018 Option Exercise
Significant agreements.
Biological Targets | item			4
Transaction price				5,650						$ 6,300		5,650
Option fee for development and exploitation rights		5,000
Number of FTE | employee	2
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								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
AstraZeneca | May 2018 Option Exercise | Commercialization license per candidate
Significant agreements.
Customer option payment		$ 8,000