Significant agreements - Cancer Research UK (Details) - USD ($) $ in Millions	Dec. 13, 2016	Jun. 30, 2019	Dec. 31, 2018
Research and development arrangement obligation to repay other parties
Contingent future milestones payments under research and development arrangement	$ 50.9
Other long term liabilities
Research and development arrangement obligation to repay other parties
Liability from research and development		$ 1.3	$ 0.8
Commercialization license per candidate
Research and development arrangement obligation to repay other parties
Refunding the costs and expenses incurred in case of termination (as a percent)	50.00%