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RESERVE FOR CLAIMS AND CLAIM EXPENSES - Schedule of Incurred and Paid Claims Development (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | $ 37,641,793 |  |  |  |  |  |  |  |  |
IBNR and ACR | 12,815,513 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 21,163,689 |  |  |  |  |  |  |  |  |
Outstanding liabilities from accident year 2014 and prior, net of reinsurance | 386,060 |  |  |  |  |  |  |  |  |
Adjustment for unallocated loss adjustment expenses | 114,425 |  |  |  |  |  |  |  |  |
Unamortized fair value and other adjustments recorded in connection with acquisitions | (156,488) |  |  |  |  |  |  |  |  |
Liability for claims and claim expenses, net of reinsurance | 16,822,101 |  |  |  |  |  |  |  |  |
Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 14,142,805 |  |  |  |  |  |  |  |  |
IBNR and ACR | 3,171,483 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 9,266,497 |  |  |  |  |  |  |  |  |
Outstanding liabilities from accident year 2014 and prior, net of reinsurance | 49,601 |  |  |  |  |  |  |  |  |
Adjustment for unallocated loss adjustment expenses | 15,115 |  |  |  |  |  |  |  |  |
Unamortized fair value and other adjustments recorded in connection with acquisitions | (34,183) |  |  |  |  |  |  |  |  |
Liability for claims and claim expenses, net of reinsurance | 4,906,841 |  |  |  |  |  |  |  |  |
Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 23,498,988 |  |  |  |  |  |  |  |  |
IBNR and ACR | 9,644,030 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 11,897,192 |  |  |  |  |  |  |  |  |
Outstanding liabilities from accident year 2014 and prior, net of reinsurance | 336,459 |  |  |  |  |  |  |  |  |
Adjustment for unallocated loss adjustment expenses | 99,310 |  |  |  |  |  |  |  |  |
Unamortized fair value and other adjustments recorded in connection with acquisitions | (122,305) |  |  |  |  |  |  |  |  |
Liability for claims and claim expenses, net of reinsurance | 11,915,260 |  |  |  |  |  |  |  |  |
Accident Year 2015 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,485,686 | $ 1,487,053 | $ 1,489,897 | $ 1,497,311 | $ 1,494,406 | $ 1,505,261 | $ 1,527,011 | $ 1,572,065 | $ 1,603,613 | $ 1,670,190
IBNR and ACR | 51,310 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,430,775 | 1,417,548 | 1,391,122 | 1,353,866 | 1,303,717 | 1,239,336 | 1,137,612 | 1,009,810 | 787,860 | 456,673
Accident Year 2015 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 373,895 | 375,420 | 376,457 | 374,258 | 383,214 | 388,076 | 397,750 | 414,379 | 456,920 | 506,243
IBNR and ACR | 511 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 370,585 | 369,874 | 365,875 | 362,864 | 360,172 | 356,090 | 344,855 | 322,118 | 277,662 | 141,410
Accident Year 2015 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,111,791 | 1,111,633 | 1,113,440 | 1,123,053 | 1,111,192 | 1,117,185 | 1,129,261 | 1,157,686 | 1,146,693 | 1,163,947
IBNR and ACR | 50,799 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,060,190 | 1,047,674 | 1,025,247 | 991,002 | 943,545 | 883,246 | 792,757 | 687,692 | 510,198 | $ 315,263
Accident Year 2016 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,768,120 | 1,762,581 | 1,784,035 | 1,752,579 | 1,734,299 | 1,811,320 | 1,843,984 | 1,882,586 | 1,872,508 |
IBNR and ACR | 31,713 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,653,636 | 1,615,296 | 1,586,304 | 1,522,045 | 1,416,750 | 1,280,778 | 1,103,921 | 895,958 | 469,972 |
Accident Year 2016 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 522,370 | 522,917 | 532,556 | 514,263 | 517,878 | 544,624 | 564,880 | 592,915 | 572,814 |
IBNR and ACR | 3,361 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 480,030 | 477,703 | 481,117 | 476,483 | 465,432 | 438,693 | 405,317 | 324,607 | 144,973 |
Accident Year 2016 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,245,750 | 1,239,664 | 1,251,479 | 1,238,316 | 1,216,421 | 1,266,696 | 1,279,104 | 1,289,671 | 1,299,694 |
IBNR and ACR | 28,352 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,173,606 | 1,137,593 | 1,105,187 | 1,045,562 | 951,318 | 842,085 | 698,604 | 571,351 | $ 324,999 |
Accident Year 2017 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 3,171,839 | 3,160,015 | 3,168,653 | 3,230,732 | 3,262,344 | 3,340,805 | 3,423,131 | 3,606,410 |  |
IBNR and ACR | 106,741 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 2,850,754 | 2,726,059 | 2,579,980 | 2,416,297 | 2,229,595 | 1,864,861 | 1,503,737 | 922,620 |  |
Accident Year 2017 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,496,890 | 1,521,356 | 1,550,274 | 1,613,614 | 1,670,648 | 1,687,873 | 1,813,187 | 1,951,429 |  |
IBNR and ACR | 76,065 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,323,316 | 1,313,624 | 1,291,080 | 1,243,652 | 1,223,434 | 1,115,451 | 935,017 | 619,039 |  |
Accident Year 2017 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,674,949 | 1,638,659 | 1,618,379 | 1,617,118 | 1,591,696 | 1,652,932 | 1,609,944 | 1,654,981 |  |
IBNR and ACR | 30,676 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,527,438 | 1,412,435 | 1,288,900 | 1,172,645 | 1,006,161 | 749,410 | 568,720 | $ 303,581 |  |
Accident Year 2018 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,980,818 | 2,965,944 | 2,926,168 | 2,934,773 | 3,065,222 | 3,132,829 | 2,912,949 |  |  |
IBNR and ACR | 178,549 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 2,382,009 | 2,238,238 | 2,118,511 | 1,900,077 | 1,593,543 | 1,190,862 | 672,825 |  |  |
Accident Year 2018 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,072,994 | 1,098,897 | 1,147,450 | 1,158,452 | 1,286,032 | 1,348,628 | 1,271,912 |  |  |
IBNR and ACR | 64,246 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 853,609 | 852,022 | 917,391 | 872,831 | 838,513 | 675,404 | 453,864 |  |  |
Accident Year 2018 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,907,824 | 1,867,047 | 1,778,718 | 1,776,321 | 1,779,190 | 1,784,201 | 1,641,037 |  |  |
IBNR and ACR | 114,303 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,528,400 | 1,386,216 | 1,201,120 | 1,027,246 | 755,030 | 515,458 | $ 218,961 |  |  |
Accident Year 2019 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,620,761 | 2,564,553 | 2,554,243 | 2,591,017 | 2,680,637 | 2,706,854 |  |  |  |
IBNR and ACR | 249,622 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 2,225,414 | 1,996,128 | 1,678,643 | 1,350,356 | 991,137 | 382,173 |  |  |  |
Accident Year 2019 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 912,496 | 914,252 | 976,162 | 1,042,748 | 1,135,337 | 1,162,088 |  |  |  |
IBNR and ACR | 35,810 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 818,617 | 777,272 | 718,321 | 632,491 | 457,281 | 164,785 |  |  |  |
Accident Year 2019 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,708,265 | 1,650,301 | 1,578,081 | 1,548,269 | 1,545,300 | 1,544,766 |  |  |  |
IBNR and ACR | 213,812 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,406,797 | 1,218,856 | 960,322 | 717,865 | 533,856 | $ 217,388 |  |  |  |
Accident Year 2020 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 4,301,296 | 4,370,007 | 4,397,548 | 4,392,922 | 4,393,340 |  |  |  |  |
IBNR and ACR | 761,291 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 3,239,789 | 2,795,075 | 2,323,405 | 1,810,464 | 756,409 |  |  |  |  |
Accident Year 2020 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,972,883 | 2,010,634 | 2,076,315 | 2,075,320 | 1,966,826 |  |  |  |  |
IBNR and ACR | 265,855 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,517,898 | 1,332,331 | 1,139,605 | 878,467 | 284,033 |  |  |  |  |
Accident Year 2020 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,328,413 | 2,359,373 | 2,321,233 | 2,317,602 | 2,426,514 |  |  |  |  |
IBNR and ACR | 495,436 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,721,891 | 1,462,744 | 1,183,800 | 931,997 | $ 472,376 |  |  |  |  |
Accident Year 2021 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 4,906,690 | 5,176,258 | 5,388,056 | 5,534,493 |  |  |  |  |  |
IBNR and ACR | 1,018,009 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 3,356,124 | 2,922,881 | 2,092,957 | 886,330 |  |  |  |  |  |
Accident Year 2021 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,440,274 | 2,655,570 | 2,758,871 | 2,759,175 |  |  |  |  |  |
IBNR and ACR | 143,701 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,984,325 | 1,852,117 | 1,371,613 | 585,175 |  |  |  |  |  |
Accident Year 2021 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,466,416 | 2,520,688 | 2,629,185 | 2,775,318 |  |  |  |  |  |
IBNR and ACR | 874,308 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,371,799 | 1,070,764 | 721,344 | $ 301,155 |  |  |  |  |  |
Accident Year 2022 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 5,128,208 | 5,627,982 | 5,902,647 |  |  |  |  |  |  |
IBNR and ACR | 2,231,524 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 2,260,464 | 1,446,448 | 280,032 |  |  |  |  |  |  |
Accident Year 2022 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 2,045,341 | 2,431,989 | 2,544,022 |  |  |  |  |  |  |
IBNR and ACR | 597,038 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,157,016 | 764,636 | 76,656 |  |  |  |  |  |  |
Accident Year 2022 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 3,082,867 | 3,195,993 | 3,358,625 |  |  |  |  |  |  |
IBNR and ACR | 1,634,486 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,103,448 | 681,812 | $ 203,376 |  |  |  |  |  |  |
Accident Year 2023 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 5,200,462 | 5,277,384 |  |  |  |  |  |  |  |
IBNR and ACR | 3,144,564 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 1,289,115 | 516,063 |  |  |  |  |  |  |  |
Accident Year 2023 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,376,749 | 1,469,539 |  |  |  |  |  |  |  |
IBNR and ACR | 577,889 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 536,495 | 232,849 |  |  |  |  |  |  |  |
Accident Year 2023 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 3,823,713 | 3,807,845 |  |  |  |  |  |  |  |
IBNR and ACR | 2,566,675 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 752,620 | $ 283,214 |  |  |  |  |  |  |  |
Accident Year 2024 |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 6,077,913 |  |  |  |  |  |  |  |  |
IBNR and ACR | 5,042,190 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 475,609 |  |  |  |  |  |  |  |  |
Accident Year 2024 | Property |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 1,928,913 |  |  |  |  |  |  |  |  |
IBNR and ACR | 1,407,007 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | 224,606 |  |  |  |  |  |  |  |  |
Accident Year 2024 | Casualty and Specialty |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Claims and Claim Expenses, Net of Reinsurance | 4,149,000 |  |  |  |  |  |  |  |  |
IBNR and ACR | 3,635,183 |  |  |  |  |  |  |  |  |
Cumulative Paid Claims and Claim Expenses, Net of Reinsurance | $ 251,003 |  |  |  |  |  |  |  |  |

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- Definition Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Unamortized Fair Value Adjustments Associated With Acquisition + References No definition available. + Details
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- Definition Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
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