v3.26.1
Reserve for Loss and Loss Expense - Schedule of Rollforward of Reserve for Loss and Loss Expense (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Gross reserve for loss and loss expense, at beginning of period $ 7,225,398 $ 6,589,801
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of period 877,843 1,022,245
Net reserve for loss and loss expense, at beginning of period 6,347,555 5,567,556
Incurred loss and loss expense for claims occurring in the:    
Current year 1,658,989 1,535,575
Prior years (27,219) 34,648
Total incurred loss and loss expense 1,631,770 1,570,223
Paid loss and loss expense for claims occurring in the:    
Current year 342,237 320,366
Prior years 884,034 865,344
Total paid loss and loss expense 1,226,271 1,185,710
Net reserve for loss and loss expense, at end of period 6,753,054 5,952,069
Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 928,385 859,087
Gross reserve for loss and loss expense, at end of period $ 7,681,439 $ 6,811,156