v3.26.1
Unpaid losses and loss adjustment expenses - Schedule of Unpaid Losses and Loss Adjustment Expenses (LAE) (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]      
Gross reserve for unpaid losses and LAE, beginning of year $ 2,005.4 $ 1,294.4  
Less: Reinsurance recoverables, beginning of year 1,682.3 1,069.5  
Net reserve for unpaid losses and LAE, beginning of year 323.1 224.9  
Reserves reassumed under commutation agreement 97.4 0.0  
Incurred losses and LAE related to:      
Current accident year 157.5 96.5  
Prior accident years (4.0) 0.0  
Total incurred losses and LAE 153.5 96.5  
Paid losses and LAE:      
Current accident year (3.9) (16.1)  
Prior accident years (40.7) (53.6)  
Total paid losses and LAE (44.6) (69.7)  
Foreign exchange adjustments (3.6) 15.7  
Retroactive reinsurance (345.0) 0.0  
Net reserve for unpaid losses and LAE, end of period 180.8 267.4  
Reinsurance recoverables on unpaid losses and LAE, end of period 2,092.9 1,424.6  
Gross reserve for unpaid losses and LAE, end of period 2,273.7 $ 1,692.0  
Gain on reinsurance commutations 7.3    
Amount received 104.7    
Commutation consideration receivable 116.7   $ 12.0
Loss portfolio transfer, retained loss reserves limit 502.0    
Loss portfolio transfer, net loss reserve, coverage 363.2    
Loss portfolio transfer, funds held under reinsurance $ 345.0