RESERVE FOR CLAIMS AND CLAIM EXPENSES - Narrative (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) |
| 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) | ||
| Baltimore Bridge Collapse | Casualty and Specialty | ||||
| Liability for Catastrophe Claims [Line Items] | ||||
| Total net (favorable) adverse development of prior accident years net claims and claim expenses | $ 50,300 | |||