Significant agreements - Genentech Collaboration Agreement (Details)		1 Months Ended	12 Months Ended
	Feb. 21, 2020 USD ($) item	Oct. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2021 USD ($)
Significant agreements.
Collaboration revenues			$ 11,697,000	$ 10,390,000	$ 13,801,000
Deferred revenue			71,340,000	35,156,000	$ 5,657,000
Genentech
Significant agreements.
Number of potential development candidates | item	4
Upfront cash payment	$ 30,000,000.0
Number of immuno oncology targets | item	2
Additional number of immuno oncology targets | item	2
Expansion Fee	$ 10,000,000.0
Sales milestone payments, receivable						$ 2,000,000.0
Transaction price	31,000,000.0		$ 33,000,000			$ 33,000,000.0
Period over which performance obligations will be performed			2 years
Material rights exercise period			4 years
Collaboration revenues			$ 5,660,000	4,896,000
Deferred revenue			$ 34,436,000	$ 27,579,000
Genentech | Royalty
Significant agreements.
Number of years over which royalty is payable			10 years
Genentech | Maximum
Significant agreements.
Regulatory, and initial commercialization milestones, payments receivable	200,000,000.0
Genentech | Development milestone | Maximum
Significant agreements.
Sales milestone payments, receivable	65,000,000.0
Genentech | Regulatory milestone | Maximum
Significant agreements.
Sales milestone payments, receivable	$ 135,000,000.0
Genentech | Collaboration Program 1 Performance Obligation
Significant agreements.
Transaction price			$ 4,019,000
Genentech | Collaboration Program 2 Performance Obligation
Significant agreements.
Transaction price			8,037,000
Genentech | Collaboration Program 3 Performance Obligation
Significant agreements.
Expansion Fee		$ 10,000,000.0
Sales milestone payments, receivable		1,000,000.0
Transaction price		11,000,000.0
Material rights		3,500,000
Collaboration revenues		6,400,000
Genentech | Specified Targeting Arm Material Right Arm Program One
Significant agreements.
Number of initial collaboration programs exercised | item	1
Sales milestone payments, receivable	$ 1,000,000.0
Customer option payment	$ 1,000,000.0
Transaction price			352,000
Genentech | Two material rights associated with the LSR Go Option for Collaboration Programs One And Two
Significant agreements.
Number of collaboration programs	2
Transaction price			12,400,000
Genentech | Material rights for associated and limited substitution rights
Significant agreements.
Transaction price			1,187,000
Deferred revenue		700,000
Genentech | Material rights associated with the LSR Go Option for Collaboration Programs Three
Significant agreements.
Deferred revenue		$ 7,400,000
Genentech | Two material rights for Expansion Options
Significant agreements.
Number of expansion option collaboration programs | item	2
Transaction price			$ 7,005,000
Genentech | Collaboration Program One and Two Performance Obligation | Maximum
Significant agreements.
Sales milestone payments, receivable	$ 200,000,000.0