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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, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | $ 3,124,486 | $ 3,012,582 | $ 9,270,669 | $ 9,164,683
Direct premiums earned | 3,118,899 | 2,928,239 | 9,096,408 | 8,791,309
Assumed premiums written | 734,407 | 459,127 | 3,950,945 | 2,959,555
Assumed premiums earned | 1,565,605 | 935,374 | 3,016,157 | 2,106,919
Ceded premiums written | (1,620,697) | (1,489,573) | (6,429,776) | (5,631,286)
Ceded premiums earned | (2,478,731) | (1,753,505) | (5,675,727) | (4,583,394)
Net premiums written | 2,238,196 | 1,982,136 | 6,791,838 | 6,492,952
Net premiums earned | 2,205,773 | 2,110,108 | 6,436,838 | 6,314,834
Underwriting [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | 2,420,107 | 2,249,500 | 6,970,879 | 6,713,503
Direct premiums earned | 2,275,753 | 2,206,453 | 6,681,520 | 6,554,464
Assumed premiums written | 382,313 | 282,089 | 1,583,225 | 1,515,639
Assumed premiums earned | 453,405 | 404,686 | 1,342,521 | 1,212,116
Ceded premiums written | (563,681) | (549,264) | (1,761,973) | (1,735,668)
Ceded premiums earned | (522,939) | (500,842) | (1,587,018) | (1,451,224)
Net premiums written | 2,238,739 | 1,982,325 | 6,792,131 | 6,493,474
Net premiums earned | 2,206,219 | 2,110,297 | 6,437,023 | 6,315,356
Fronting |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Direct premiums written | 704,379 | 763,082 | 2,299,790 | 2,451,180
Direct premiums earned | 843,146 | 721,786 | 2,414,888 | 2,236,845
Assumed premiums written | 352,094 | 177,038 | 2,367,720 | 1,443,916
Assumed premiums earned | 1,112,200 | 530,688 | 1,673,636 | 894,803
Ceded premiums written | (1,057,016) | (940,309) | (4,667,803) | (3,895,618)
Ceded premiums earned | (1,955,792) | (1,252,663) | (4,088,709) | (3,132,170)
Net premiums written | (543) | (189) | (293) | (522)
Net premiums earned | $ (446) | $ (189) | $ (185) | $ (522)

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