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Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred Policy Acquisition Cost | $ 951,728 | $ 861,609 | $ 763,486
Reserve for Losses and Loss Expenses | 20,368,030 | 18,739,652 | 17,011,223
Unearned Premiums | 6,375,112 | 5,922,326 | 5,297,654
Net Premiums Earned | 11,548,485 | 10,400,687 | 9,561,429
Net Investment Income | 1,333,161 | 1,052,835 | 779,185
Loss and Loss Expenses | 7,131,595 | 6,372,142 | 5,861,750
Amortization of Deferred Policy Acquisition Cost | 1,219,849 | 1,038,975 | 1,038,903
Other Operating Costs and Expenses | 2,382,457 | 2,324,961 | 1,922,602
Net Premiums Written | 11,972,096 | 10,954,467 | 10,004,070
Operating Segments | Insurance |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred Policy Acquisition Cost | 840,917 | 736,348 | 633,493
Reserve for Losses and Loss Expenses | 16,887,821 | 15,298,372 | 13,655,613
Unearned Premiums | 5,836,435 | 5,322,869 | 4,708,586
Net Premiums Earned | 10,086,308 | 9,007,376 | 8,171,828
Net Investment Income | 1,057,738 | 783,660 | 543,844
Loss and Loss Expenses | 6,332,490 | 5,615,526 | 5,013,614
Amortization of Deferred Policy Acquisition Cost | 1,081,170 | 897,908 | 881,567
Other Operating Costs and Expenses | 1,825,758 | 1,684,514 | 1,418,374
Net Premiums Written | 10,549,550 | 9,560,533 | 8,609,028
Operating Segments | Reinsurance & Monoline Excess |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred Policy Acquisition Cost | 110,811 | 125,261 | 129,993
Reserve for Losses and Loss Expenses | 3,480,209 | 3,441,280 | 3,355,610
Unearned Premiums | 538,677 | 599,457 | 589,068
Net Premiums Earned | 1,462,177 | 1,393,311 | 1,389,601
Net Investment Income | 234,728 | 221,966 | 200,512
Loss and Loss Expenses | 799,105 | 756,616 | 848,136
Amortization of Deferred Policy Acquisition Cost | 138,679 | 141,067 | 157,336
Other Operating Costs and Expenses | 292,526 | 268,309 | 247,918
Net Premiums Written | 1,422,546 | 1,393,934 | 1,395,042
Corporate, other and eliminations |  |  |
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items] |  |  |
Deferred Policy Acquisition Cost | 0 | 0 | 0
Reserve for Losses and Loss Expenses | 0 | 0 | 0
Unearned Premiums | 0 | 0 | 0
Net Premiums Earned | 0 | 0 | 0
Net Investment Income | 40,695 | 47,209 | 34,829
Loss and Loss Expenses | 0 | 0 | 0
Amortization of Deferred Policy Acquisition Cost | 0 | 0 | 0
Other Operating Costs and Expenses | 264,173 | 372,138 | 256,310
Net Premiums Written | $ 0 | $ 0 | $ 0

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