RESERVE FOR LOSSES AND LOSS EXPENSES - Incurred Losses Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Additional Information Related to Net Incurred Losses [Line Items]
Net losses and loss expenses, net of reinstatement premiums	$ 3,267,943	$ 3,041,193	$ 3,297,161
Foreign exchange and other	685,132	39,174	(211,949)
Syndicate 2007
Additional Information Related to Net Incurred Losses [Line Items]
Foreign exchange and other		(49,000)
Third Party - Loss Portfolio Transfer
Additional Information Related to Net Incurred Losses [Line Items]
Foreign exchange and other	(422,000)
Catastrophe and Weather-related Events
Additional Information Related to Net Incurred Losses [Line Items]
Net losses and loss expenses, net of reinstatement premiums	$ 403,000	$ 443,000	$ 774,000