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Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | $ 2,839,412 | $ 2,797,453 | $ 8,491,896 | $ 8,091,131
Direct premiums earned | 2,796,788 | 2,629,128 | 8,084,663 | 7,406,497
Assumed premiums written | 839,394 | 677,318 | 2,411,107 | 2,061,976
Assumed premiums earned | 737,699 | 627,000 | 1,794,614 | 1,526,919
Ceded premiums written | (1,651,001) | (1,465,604) | (4,449,727) | (3,879,411)
Ceded premiums earned | (1,412,742) | (1,299,298) | (3,758,685) | (3,383,712)
Net premiums written | 2,027,805 | 2,009,167 | 6,453,276 | 6,273,696
Net premiums earned | 2,121,745 | 1,956,830 | 6,120,592 | 5,549,704
Underwriting [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | 2,223,988 | 2,133,822 | 6,479,090 | 6,065,936
Direct premiums earned | 2,127,244 | 1,899,816 | 6,124,444 | 5,370,481
Assumed premiums written | 282,070 | 349,650 | 1,419,802 | 1,466,036
Assumed premiums earned | 424,620 | 408,561 | 1,247,743 | 1,194,504
Ceded premiums written | (478,035) | (473,885) | (1,444,626) | (1,255,226)
Ceded premiums earned | (429,901) | (351,118) | (1,250,605) | (1,012,485)
Net premiums written | 2,028,023 | 2,009,587 | 6,454,266 | 6,276,746
Net premiums earned | 2,121,963 | 1,957,259 | 6,121,582 | 5,552,500
Program services and other fronting [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | 615,424 | 663,631 | 2,012,806 | 2,025,195
Direct premiums earned | 669,544 | 729,312 | 1,960,219 | 2,036,016
Assumed premiums written | 557,324 | 327,668 | 991,305 | 595,940
Assumed premiums earned | 313,079 | 218,439 | 546,871 | 332,415
Ceded premiums written | (1,172,966) | (991,719) | (3,005,101) | (2,624,185)
Ceded premiums earned | (982,841) | (948,180) | (2,508,080) | (2,371,227)
Net premiums written | (218) | (420) | (990) | (3,050)
Net premiums earned | $ (218) | $ (429) | $ (990) | $ (2,796)

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