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	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2025	Dec. 31, 2024
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross liability for losses and loss settlement expenses at beginning of year		$ 1,796,782	$ 1,638,755
Ceded losses and loss settlement expenses		(198,083)	(191,640)
Net liability for losses and loss settlement expenses at beginning of year		1,598,699	1,447,115
Losses and loss settlement expenses incurred for claims occurring during
Current year		585,403	745,813
Prior years	$ (1,900)	(13,795)	(1,208)
Total incurred		571,608	744,605
Losses and loss settlement expense payments for claims occurring during
Current year		137,516	186,322
Prior years		355,983	406,699
Total paid		493,499	593,021
Net liability for losses and loss settlement expenses at end of period	1,676,808	1,676,808	1,598,699
Ceded losses and loss settlement expenses	205,259	205,259	198,083
Gross liability for losses and loss settlement expenses at end of period	$ 1,882,067	$ 1,882,067	$ 1,796,782