Significant agreements - Cancer Research UK (Details) - USD ($) $ in Millions		1 Months Ended
	Dec. 13, 2016	Dec. 31, 2019	Mar. 31, 2024	Dec. 31, 2023
Research and development arrangement obligation to repay other parties
Contingent future milestones payments under research and development arrangement	$ 50.9	$ 60.3
Other long term liabilities
Research and development arrangement obligation to repay other parties
Liability from research and development			$ 4.3	$ 4.3
BT1718 | Minimum
Research and development arrangement obligation to repay other parties
Tiered royalties (percentage)	70.00%
BT1718 | Maximum
Research and development arrangement obligation to repay other parties
Tiered royalties (percentage)	90.00%
BT7401 | Minimum
Research and development arrangement obligation to repay other parties
Tiered royalties (percentage)		55.00%
BT7401 | Maximum
Research and development arrangement obligation to repay other parties
Tiered royalties (percentage)		80.00%