v3.26.3
Loss and loss adjustment expense reserves - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Disposal Group, Including Discontinued Operations [Line Items]          
Prior year loss reserve development $ (19.8) $ (8.9) $ (52.7) $ (51.8)  
Funds held liability 164.6   164.6    
Reinsurance balances payable 1,472.5   1,472.5   $ 1,447.6
Pallas Reinsurance Company Ltd.          
Disposal Group, Including Discontinued Operations [Line Items]          
Reinsurance balances payable $ 271.2   $ 271.2