v3.26.1
RESERVE FOR LOSSES AND LOSS EXPENSES - Reserve Roll-Forward (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]        
Gross reserve for losses and loss expenses, beginning of period     $ 18,122,256 $ 17,218,929
Less reinsurance recoverable on unpaid losses and loss expenses, beginning of period     (8,951,763) (6,840,897)
Net reserve for unpaid losses and loss expenses, beginning of period     9,170,493 10,378,032
Net incurred losses and loss expenses related to:        
Current year     1,833,311 1,625,845
Prior years $ (14,836) $ (20,229) (32,899) (38,166)
Net incurred losses and loss expenses 933,130 801,754 1,800,412 1,587,679
Net paid losses and loss expenses related to:        
Current year     (196,928) (166,553)
Prior years     (1,233,370) (1,395,871)
Net paid losses and loss expenses     (1,430,298) (1,562,424)
Foreign exchange and other     (61,837) 291,481
Ceded reserves related to retroactive transactions     185,620 (1,902,645)
Reinsurance recoverable on unpaid losses     123,783 (1,611,164)
Net reserve for unpaid losses and loss expenses, end of period 9,664,390 8,792,123 9,664,390 8,792,123
Reinsurance recoverable on unpaid losses and loss expenses, end of period 8,949,022 9,086,900 8,949,022 9,086,900
Gross reserve for losses and loss expenses, end of period $ 18,613,412 $ 17,879,023 $ 18,613,412 $ 17,879,023