Significant agreements - Novartis Collaboration Agreement - Accounting Analysis (Details) $ in Thousands		3 Months Ended
	Mar. 27, 2023 USD ($) item	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues		$ 19,530	$ 4,896
Deferred revenue		114,547		$ 135,194	$ 61,873
Novartis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction price	$ 50,000
Collaboration revenues		1,247	$ 0
Deferred revenue		$ 48,341		$ 50,008
Novartis | Two Combined Performance Obligations For First And Second Targets [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Combined performance obligations | item	2
Transaction price	$ 18,008
Novartis | Two Material Rights Associated With Limited Substitution Rights [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of material rights | item	2
Transaction price	$ 2,466
Novartis | Two Material Rights Associated With Options To Progress Development Candidates Incorporating Radionuclides [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of material rights | item	2
Transaction price	$ 19,684
Novartis | Two Material Rights Associated With Options To Progress Development Candidates Not Incorporating Radionuclides [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of material rights | item	2
Transaction price	$ 9,842