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v3.25.3

Business Segments (Net Premiums Earned By Major Line of Business) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | $ 3,156,382 | $ 2,926,823 | $ 9,266,948 | $ 8,537,585
Insurance |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums |  | 2,564,490 |  | 7,447,828
Insurance | Operating Segments |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 2,773,009 | 2,564,490 | 8,144,300 | 7,447,828
Insurance | Other liability |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 1,122,591 | 1,031,087 | 3,299,651 | 3,000,335
Insurance | Short-tail lines |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 636,751 | 563,736 | 1,852,847 | 1,613,342
Insurance | Auto |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 408,213 | 376,762 | 1,203,794 | 1,092,354
Insurance | Workers' compensation |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 318,284 | 313,154 | 948,194 | 925,214
Insurance | Professional liability |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 287,170 | 279,751 | 839,814 | 816,583
Reinsurance & Monoline Excess |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums |  | 362,333 |  | 1,089,757
Reinsurance & Monoline Excess | Operating Segments |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 383,373 | 362,333 | 1,122,648 | 1,089,757
Reinsurance & Monoline Excess | Casualty |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 189,767 | 188,284 | 556,437 | 585,208
Reinsurance & Monoline Excess | Monoline excess |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | 74,339 | 65,663 | 212,965 | 196,525
Reinsurance & Monoline Excess | Property |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Earned premiums | $ 119,267 | $ 108,386 | $ 353,246 | $ 308,024

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