v3.26.3
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, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses $ (267,145) $ (380,051) $ (628,585) $ (845,635)
Amortization of fair value adjustments     22,100 30,900
Actuarial assumption changes        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses       (33,100)
Property        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (683,245) (837,307)
Property | Actuarial assumption changes        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (25,700)  
Property | Large catastrophe events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (358,411) (433,836)
Property | 2025 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (31,212) 0
Property | 2024 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (146,291) (43,057)
Property | 2023 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (41,235) (77,391)
Property | 2022 Weather-Related Large Losses        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (72,419) (207,672)
Property | 2021 Weather-Related Large Losses        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (46,275) (29,458)
Property | 2020 Weather-Related Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (3,774) (10,629)
Property | 2019 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (3,598) (8,233)
Property | 2018 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (6,993) (20,089)
Property | 2017 Large Loss Events        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (6,614) (37,307)
Property | Total small catastrophe events and attritional loss movements        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (299,134) (370,371)
Amortization of fair value adjustments     5,500 7,700
Property | Total catastrophe and attritional net claims and claim expenses        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (657,545) (804,207)
Casualty and Specialty        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     54,660 (8,328)
Casualty and Specialty | Actuarial assumption changes        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     95,826 19,839
Casualty and Specialty | Actuarial methods - actual reported claims less than expected claims        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses     (41,166) (28,167)
Amortization of fair value adjustments     16,600 23,100
Operating Segments | Property        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses (265,032) (383,673) (683,245) (837,307)
Operating Segments | Casualty and Specialty        
Liability for Catastrophe Claims [Line Items]        
Total net (favorable) adverse development of prior accident years net claims and claim expenses $ (2,113) $ 3,622 $ 54,660 $ (8,328)