v3.25.1
Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Dec. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]        
Loss and loss adjustment expenses $ 261.8 $ 185.8    
Other Operations        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Loss and loss adjustment expense reserves 13.4   $ 12.1  
Loss and loss adjustment expenses 17.4 0.0    
P&C Insurance and Reinsurance (Ark/WM Outrigger)        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Prior year losses (52.8) (0.3)    
Loss and loss adjustment expense reserves 2,253.9 1,744.5 2,127.5 $ 1,605.1
Loss and loss adjustment expenses 233.5 180.0    
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Loss and loss adjustment expense reserves 2,253.9   2,127.5  
Loss and loss adjustment expenses 233.5 180.0    
P&C Insurance Distribution (Bamboo)        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Loss and loss adjustment expenses 10.9 5.8    
P&C Insurance Distribution (Bamboo) | Operating Segments        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Loss and loss adjustment expense reserves 23.2   $ 17.8  
Loss and loss adjustment expenses $ 10.9 $ 5.8