RESERVE FOR LOSSES AND LOSS EXPENSES - Reserve Roll-Forward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserve for losses and loss expenses, beginning of period			$ 15,168,863	$ 14,653,094
Less reinsurance recoverable on unpaid losses and loss expenses, beginning of period			(5,831,172)	(5,017,611)
Net reserve for unpaid losses and loss expenses, beginning of period			9,337,691	9,635,483
Net incurred losses and loss expenses related to:
Current year			1,467,256	1,515,182
Prior years	$ (6,319)	$ (3,940)	(10,357)	(12,897)
Net incurred losses and loss expenses	736,257	769,587	1,456,899	1,502,285
Net paid losses and loss expenses related to:
Current year			(129,414)	(120,713)
Prior years			(1,210,101)	(1,354,605)
Net paid losses and loss expenses			(1,339,515)	(1,475,318)
Foreign exchange and other			98,814	(272,994)
Net reserve for unpaid losses and loss expenses, end of period	9,553,889	9,389,456	9,553,889	9,389,456
Reinsurance recoverable on unpaid losses and loss expenses, end of period	5,865,609	5,008,583	5,865,609	5,008,583
Gross reserve for losses and loss expenses, end of period	$ 15,419,498	$ 14,398,039	$ 15,419,498	$ 14,398,039