v3.25.2
Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Mar. 31, 2025
Dec. 31, 2024
Mar. 31, 2024
Dec. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]                
Loss and loss adjustment expenses $ 166.5 $ 183.9 $ 428.3 $ 369.7        
Other Operations                
Liability for Claims and Claims Adjustment Expense [Line Items]                
Loss and loss adjustment expense reserves 14.2   14.2     $ 12.1    
Loss and loss adjustment expenses 0.8 3.9 18.2 3.9        
P&C Insurance and Reinsurance (Ark/WM Outrigger)                
Liability for Claims and Claims Adjustment Expense [Line Items]                
Prior year losses (17.1) (6.9) (69.9) (7.2)        
Loss and loss adjustment expense reserves 2,288.5 1,890.1 2,288.5 1,890.1 $ 2,253.9 2,127.5 $ 1,744.5 $ 1,605.1
Loss and loss adjustment expenses 164.0 175.7 397.5 355.7        
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 2,288.5   2,288.5     2,127.5    
Loss and loss adjustment expenses 164.0 175.7 397.5 355.7        
P&C Insurance Distribution (Bamboo)                
Liability for Claims and Claims Adjustment Expense [Line Items]                
Loss and loss adjustment expenses 1.7 12.6 4.3 10.1        
P&C Insurance Distribution (Bamboo) | Operating Segments                
Liability for Claims and Claims Adjustment Expense [Line Items]                
Loss and loss adjustment expense reserves 28.8   28.8     $ 17.8    
Loss and loss adjustment expenses $ 1.7 $ 4.3 $ 12.6 $ 10.1