RESERVE FOR CLAIMS AND CLAIM EXPENSES - Prior Year Development of the Reserve for Net Claims and Claim Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	$ (104,752)	$ (17,833)
Property
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(81,693)	(16,758)
Property | Large and Small Catastrophe Events and Attritional Loss Movements
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(81,693)	(16,758)
Property | Large catastrophe events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(76,607)	(14,290)
Property | 2022 Weather-Related Large Losses
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(7,785)
Property | 2021 Weather-Related Large Lossses
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(32,333)	19,190
Property | 2020 Weather-Related Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	6,535	(5,272)
Property | 2019 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(15,369)	(4,807)
Property | 2018 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(16,259)	(3,800)
Property | 2017 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(11,486)	(18,000)
Property | Other
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	90	(1,601)
Property | Small catastrophe events and attritional loss movements
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(5,086)	(2,468)
Property | Other small catastrophe events and attritional loss movements
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(5,086)	(2,468)
Property | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(81,693)	(16,758)
Casualty and Specialty
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(23,059)	(1,075)
Casualty and Specialty | Actuarial methods - actual reported claims less than expected claims
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(23,059)	(1,075)
Casualty and Specialty | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	$ (23,059)	$ (1,075)