RESERVE FOR CLAIMS AND CLAIM EXPENSES - Schedule of Prior Year Development of the Reserve for Net Claims and Claim Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	$ (157,947)	$ (31,906)	$ (294,797)	$ (92,696)
Property
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(257,209)	(76,069)
Property | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			840
Property | Large catastrophe events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(164,658)	(81,976)
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			6,501
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			(24,931)	42,766
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			(28,824)	(32,988)
Property | 2019 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(37,934)	(50,148)
Property | 2018 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(37,847)	(15,493)
Property | 2017 Large Loss Events
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(31,922)	(28,722)
Property | New Zealand Earthquake (2010)
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(10,397)
Property | Other
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			696	2,609
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			(92,551)	5,907
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			(93,391)	5,907
Property | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	(143,877)	(24,259)	(257,209)	(76,069)
Casualty and Specialty
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			(37,588)	(16,627)
Casualty and Specialty | Actuarial assumption changes
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses			2,910	21,512
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			(40,498)	(38,139)
Casualty and Specialty | Operating Segments
Liability for Catastrophe Claims [Line Items]
Net (favorable) adverse development of prior accident years net claims and claim expenses	$ (14,070)	$ (7,647)	$ (37,588)	$ (16,627)