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Industry Segments (Financial Information of Company Operating Segments) (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 USD ($) segment | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Segment Reporting Information [Line Items] |  |  |
Number of reportable segments | segment | 2 |  |
Earned Premiums | $ 11,548,485 | $ 10,400,687 | $ 9,561,429
Investment Income | 1,333,161 | 1,052,835 | 779,185
Net investment gains | 117,708 | 47,042 | 202,397
Other Revenues | 757,106 | 689,416 | 825,885
Total revenues | 13,638,752 | 12,142,938 | 11,166,499
Losses and Loss Expenses | 7,131,595 | 6,372,142 | 5,861,750
Policy Acquisition and Insurance Operating Expenses | 3,294,902 | 2,954,686 | 2,673,903
Other | 947,762 | 1,061,707 | 911,165
Total operating costs and expenses | 11,374,259 | 10,388,535 | 9,446,818
Pre-Tax Income (Loss) | 2,264,493 | 1,754,403 | 1,719,681
Net income to common stockholders | 1,756,115 | 1,381,359 | 1,381,062
Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 10,086,308 | 9,007,376 | 8,171,828
Reinsurance & Monoline Excess |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 1,462,177 | 1,393,311 | 1,389,601
Operating Segments | Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 10,086,308 | 9,007,376 | 8,171,828
Investment Income | 1,057,738 | 783,660 | 543,844
Other Revenues | 37,455 | 36,830 | 33,347
Total revenues | 11,181,501 | 9,827,866 | 8,749,019
Losses and Loss Expenses | 6,332,490 | 5,615,526 | 5,013,614
Policy Acquisition and Insurance Operating Expenses | 2,863,697 | 2,545,310 | 2,268,649
Other | 43,231 | 37,112 | 31,294
Total operating costs and expenses | 9,239,418 | 8,197,948 | 7,313,557
Pre-Tax Income (Loss) | 1,942,083 | 1,629,918 | 1,435,462
Net income to common stockholders | 1,503,875 | 1,283,281 | 1,153,231
Operating Segments | Reinsurance & Monoline Excess |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 1,462,177 | 1,393,311 | 1,389,601
Investment Income | 234,728 | 221,966 | 200,512
Other Revenues | 0 | 0 | 0
Total revenues | 1,696,905 | 1,615,277 | 1,590,113
Losses and Loss Expenses | 799,105 | 756,616 | 848,136
Policy Acquisition and Insurance Operating Expenses | 431,205 | 409,376 | 405,254
Total operating costs and expenses | 1,230,310 | 1,165,992 | 1,253,390
Pre-Tax Income (Loss) | 466,595 | 449,285 | 336,723
Net income to common stockholders | 367,569 | 355,155 | 271,580
Corporate, other and eliminations |  |  |
Segment Reporting Information [Line Items] |  |  |
Investment Income | 40,695 | 47,209 | 34,829
Other Revenues | 601,943 | 605,544 | 590,141
Total revenues | 642,638 | 652,753 | 624,970
Other | 904,531 | 1,024,595 | 879,871
Total operating costs and expenses | 904,531 | 1,024,595 | 879,871
Pre-Tax Income (Loss) | (261,893) | (371,842) | (254,901)
Net income to common stockholders | (203,832) | (293,869) | (203,476)
Net investment gains |  |  |
Segment Reporting Information [Line Items] |  |  |
Net investment gains | 117,708 | 47,042 | 202,397
Pre-Tax Income (Loss) | 117,708 | 47,042 | 202,397
Net income to common stockholders | $ 88,503 | $ 36,792 | $ 159,727

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