RESERVE FOR CLAIMS AND CLAIM EXPENSES - Schedule of Reserve for Claims and Claim Expenses by Segment (Details) - USD ($) $ in Thousands |
Sep. 30, 2026 |
Dec. 31, 2025 |
Sep. 30, 2025 |
|---|---|---|---|
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Case Reserves | $ 5,379,221 | $ 5,190,878 | |
| ACR | 1,558,545 | 2,007,789 | |
| IBNR | 15,356,429 | 15,103,678 | |
| Total | 22,294,195 | 22,302,345 | $ 22,712,860 |
| Operating Segments | Property | |||
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Case Reserves | 1,578,831 | 1,797,427 | |
| ACR | 1,216,667 | 1,679,848 | |
| IBNR | 1,851,913 | 2,208,709 | |
| Total | 4,647,411 | 5,685,984 | |
| Operating Segments | Casualty and Specialty | |||
| Liability for Claims and Claims Adjustment Expense [Line Items] | |||
| Case Reserves | 3,800,390 | 3,393,451 | |
| ACR | 341,878 | 327,941 | |
| IBNR | 13,504,516 | 12,894,969 | |
| Total | $ 17,646,784 | $ 16,616,361 |