RESERVE FOR LOSSES AND LOSS EXPENSES - Reserve Roll-Forward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserve for losses and loss expenses, beginning of period			$ 17,218,929	$ 16,434,018
Less reinsurance recoverable on unpaid losses and loss expenses, beginning of period			(6,840,897)	(6,323,083)
Net reserve for unpaid losses and loss expenses, beginning of period			10,378,032	10,110,935
Net incurred losses and loss expenses related to:
Current year			1,625,845	1,494,659
Prior years	$ (20,229)	$ 0	(38,166)	0
Net incurred losses and loss expenses	801,754	765,988	1,587,679	1,494,659
Net paid losses and loss expenses related to:
Current year			(166,553)	(159,455)
Prior years			(1,395,871)	(1,251,637)
Net paid losses and loss expenses			(1,562,424)	(1,411,092)
Reinsurance recoverable on unpaid losses			(1,611,164)	(47,452)
Net reserve for unpaid losses and loss expenses, end of period	8,792,123	10,147,050	8,792,123	10,147,050
Reinsurance recoverable on unpaid losses and loss expenses, end of period	9,086,900	6,591,821	9,086,900	6,591,821
Gross reserve for losses and loss expenses, end of period	$ 17,879,023	$ 16,738,871	$ 17,879,023	$ 16,738,871