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RESERVES FOR LOSSES AND LOSS SETTLEMENT EXPENSES - Changes in Property and Casualty Losses and Loss Settlement Expense Reserves (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Gross liability for losses and loss settlement expenses at beginning of year $ 1,924,826 $ 1,796,782
Ceded losses and loss settlement expenses (213,633) (198,083)
Net liability for losses and loss settlement expenses at beginning of year 1,711,193 1,598,699
Losses and loss settlement expenses incurred for claims occurring during    
Current year 208,346 778,480
Prior years (221) (14,078)
Total incurred 208,125 764,402
Losses and loss settlement expense payments for claims occurring during    
Current year 20,905 194,149
Prior years 144,347 457,759
Total paid 165,252 651,908
Net liability for losses and loss settlement expenses at end of period 1,754,065 1,711,193
Ceded losses and loss settlement expenses 216,192 213,633
Gross liability for losses and loss settlement expenses at end of period $ 1,970,257 $ 1,924,826