Significant agreements - Genentech Collaboration Agreement (Details) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 21, 2020 USD ($) item	May 31, 2018 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) item	Sep. 30, 2020 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Significant agreements.
Option fee for development and exploitation rights		$ 5,000
Collaboration revenues			$ 4,333	$ 3,842	$ 7,926	$ 6,542
Deferred revenue			62,507		62,507			$ 35,156	$ 5,657
Genentech
Significant agreements.
Number of potential development candidates | item	4
Upfront cash payment	$ 30,000
Number of immuno oncology targets | item	2
Additional number of immuno oncology targets | item	2
Expansion Fee	$ 10,000
Sales milestone payments, receivable							$ 2,000
Transaction price	31,000		33,000		$ 33,000		$ 33,000
Option fee for development and exploitation rights	30,000
Period over which performance obligations will be performed					2 years
Material rights exercise period					4 years
Collaboration revenues			1,063	$ 1,209	$ 4,142	$ 3,066
Deferred revenue			25,090		$ 25,090			$ 27,579	$ 0
Genentech | Royalty
Significant agreements.
Number of years over which royalty is payable					10 years
Genentech | Maximum
Significant agreements.
Sales milestone payments, receivable	200,000
Genentech | Development milestone | Maximum
Significant agreements.
Sales milestone payments, receivable	65,000
Genentech | Regulatory milestone | Maximum
Significant agreements.
Sales milestone payments, receivable	$ 135,000
Genentech | Collaboration Program 1 Performance Obligation
Significant agreements.
Transaction price			4,019		$ 4,019
Genentech | Collaboration Program 2 Performance Obligation
Significant agreements.
Transaction price			8,037		8,037
Genentech | Specified Targeting Arm Material Right Arm Program One
Significant agreements.
Number of initial collaboration programs exercised | item	1
Sales milestone payments, receivable	$ 1,000
Transaction price			352		$ 352
Genentech | Two material rights associated with the LSR Go Option for Collaboration Programs One And Two
Significant agreements.
Number of expansion option collaboration programs | item					2
Number of collaboration programs | item	2				2
Transaction price			12,400		$ 12,400
Genentech | Material rights for associated and limited substitution rights
Significant agreements.
Transaction price			1,187		1,187
Genentech | Two material rights for Expansion Options
Significant agreements.
Number of expansion option collaboration programs | item	2
Transaction price			$ 7,005		$ 7,005
Genentech | Collaboration Program One and Two Performance Obligation | Maximum
Significant agreements.
Regulatory, and initial commercialization milestones, payments receivable	$ 200,000