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Industry Segments (Financial Information of Company Operating Segments) (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 USD ($) segment | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items] |  |  |
Number of reportable segments | segment | 2 |  |
Earned Premiums | $ 10,400,687 | $ 9,561,429 | $ 8,106,031
Investment Income | 1,052,835 | 779,185 | 671,618
Net investment gains | 47,042 | 202,397 | 90,632
Other Revenues | 689,416 | 825,885 | 677,817
Total revenues | 12,142,938 | 11,166,499 | 9,455,466
Pre-Tax Income (Loss) | 1,754,403 | 1,719,681 | 1,282,905
Net investment gains | 36,792 | 159,727 | 72,922
Net income to common stockholders | 1,381,359 | 1,381,062 | 1,022,490
Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 9,130,324 | 8,369,062 | 7,077,708
Reinsurance & Monoline Excess |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 1,270,363 | 1,192,367 | 1,028,323
Operating Segments | Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 9,130,324 | 8,369,062 | 7,077,708
Investment Income | 793,998 | 550,084 | 468,821
Other Revenues | 36,830 | 33,347 | 32,063
Total revenues | 9,961,152 | 8,952,493 | 7,578,592
Pre-Tax Income (Loss) | 1,640,438 | 1,455,658 | 1,219,798
Net income to common stockholders | 1,291,654 | 1,173,425 | 976,184
Operating Segments | Reinsurance & Monoline Excess |  |  |
Segment Reporting Information [Line Items] |  |  |
Earned Premiums | 1,270,363 | 1,192,367 | 1,028,323
Investment Income | 211,628 | 194,272 | 175,324
Other Revenues | 0 | 0 | 0
Total revenues | 1,481,991 | 1,386,639 | 1,203,647
Pre-Tax Income (Loss) | 438,765 | 316,527 | 270,563
Net income to common stockholders | 346,782 | 251,386 | 215,439
Corporate, other and eliminations |  |  |
Segment Reporting Information [Line Items] |  |  |
Investment Income | 47,209 | 34,829 | 27,473
Other Revenues | 605,544 | 590,141 | 555,122
Total revenues | 652,753 | 624,970 | 582,595
Pre-Tax Income (Loss) | (371,842) | (254,901) | (298,088)
Net income to common stockholders | $ (293,869) | $ (203,476) | $ (242,055)

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