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v3.25.2

Business Segments (Net Premiums Earned By Major Line of Business) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | $ 3,098,185 | $ 2,846,415 | $ 6,110,566 | $ 5,610,762
Insurance |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned |  | 2,484,569 |  | 4,883,338
Insurance | Operating Segments |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 2,728,784 | 2,484,569 | 5,371,291 | 4,883,338
Insurance | Other liability |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 1,104,332 | 1,001,987 | 2,177,060 | 1,969,247
Insurance | Short-tail lines |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 619,988 | 538,797 | 1,216,096 | 1,049,606
Insurance | Auto |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 405,632 | 361,580 | 795,581 | 715,593
Insurance | Workers' compensation |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 318,881 | 310,564 | 629,910 | 612,060
Insurance | Professional liability |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 279,951 | 271,641 | 552,644 | 536,832
Reinsurance and Monoline Excess Segment |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned |  | 361,846 |  | 727,424
Reinsurance and Monoline Excess Segment | Operating Segments |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 369,401 | 361,846 | 739,275 | 727,424
Reinsurance and Monoline Excess Segment | Casualty |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 184,903 | 199,080 | 366,670 | 396,924
Reinsurance and Monoline Excess Segment | Monoline excess |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | 71,362 | 65,511 | 138,626 | 130,862
Reinsurance and Monoline Excess Segment | Property |  |  |  |
Revenue from External Customer [Line Items] |  |  |  |
Net premiums earned | $ 113,136 | $ 97,255 | $ 233,979 | $ 199,638

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