RESERVE FOR LOSSES AND LOSS EXPENSES - Summary of Reserve Roll-Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Beginning and Ending Gross Unpaid Losses and Loss Expenses
Gross reserve for losses and loss expenses, beginning of year	$ 14,653,094	$ 13,926,766	$ 12,752,081
Less reinsurance recoverable on unpaid losses, beginning of year	(5,017,611)	(4,496,641)	(3,877,756)
Net reserve for unpaid losses and loss expenses, beginning of year	9,635,483	9,430,125	8,874,325
Net incurred losses and loss expenses related to:
Current year	3,267,943	3,041,193	3,297,161
Prior years	(25,533)	(32,410)	(15,909)
Net incurred losses and loss expenses	3,242,410	3,008,783	3,281,252
Net paid losses and loss expenses related to:
Current year	(457,857)	(490,011)	(571,442)
Prior years	(2,397,213)	(2,274,240)	(2,365,959)
Net paid losses and loss expenses	(2,855,070)	(2,764,251)	(2,937,401)
Foreign exchange and other	(685,132)	(39,174)	211,949
Net reserve for unpaid losses and loss expenses, end of year	9,337,691	9,635,483	9,430,125
Reinsurance recoverable on unpaid losses, end of year	5,831,172	5,017,611	4,496,641
Gross reserve for losses and loss expenses, end of year	$ 15,168,863	$ 14,653,094	$ 13,926,766