v3.25.2
Share-based awards - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
6 Months Ended 74 Months Ended
Jun. 30, 2025
Oct. 25, 2024
May 11, 2015
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
May 16, 2019
Employee Stock Option              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Number of shares exercisable (in shares) 436,041     436,041   436,041  
Weighted average contractual term of options exercisable 3 years 18 days            
Weighted average exercise price of options exercisble (USD per share) $ 152.79     $ 152.79   $ 152.79  
Restricted stock units 2013              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Additional ordinary shares which have been reserved for issuance (in shares)   2,500,000 2,500,000        
Ordinary shares which have been reserved for issuance (in shares)   6,600,000          
Consultants Restricted Stock Units 2019              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Ordinary shares which have been reserved for issuance (in shares)             250,000
Consultants Restricted Stock Units 2019 | Non-executive directors              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Shares vesting period           12 months  
Performance Share Unit (PSUs)              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Fair value of stock units vested       $ 1.9 $ 1.8    
Restricted Stock Units (RSUs)              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Fair value of stock units vested       7.1 24.3    
Fair value of stock units granted       149.2 75.7    
Restricted Stock Units (RSUs) | Within next 12 months              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Fair value of stock units granted       $ 73.9 $ 1.5    
PSUs based on service and EPS targets | Maximum              
Compensation Related Costs Share Based Payments Disclosure [Line Items]              
Stock units to be granted (in shares) 125,091     125,091   125,091