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Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Effects of Reinsurance [Line Items] |  |
Direct premiums written | $ 2,909,657 | $ 2,852,425
Direct premiums earned | 2,934,728 | 2,901,920
Assumed premiums written | 1,308,573 | 1,087,974
Assumed premiums earned | 682,351 | 516,213
Ceded premiums written | (1,907,939) | (1,708,362)
Ceded premiums earned | (1,527,705) | (1,290,506)
Net premiums written | 2,310,291 | 2,232,037
Net premiums earned | 2,089,374 | 2,127,627
Underwriting [Member] |  |
Effects of Reinsurance [Line Items] |  |
Direct premiums written | 2,135,972 | 2,107,467
Direct premiums earned | 2,195,483 | 2,198,238
Assumed premiums written | 729,042 | 668,699
Assumed premiums earned | 438,045 | 392,942
Ceded premiums written | (554,725) | (543,956)
Ceded premiums earned | (544,156) | (463,380)
Net premiums written | 2,310,289 | 2,232,210
Net premiums earned | 2,089,372 | 2,127,800
Fronting |  |
Effects of Reinsurance [Line Items] |  |
Direct premiums written | 773,685 | 744,958
Direct premiums earned | 739,245 | 703,682
Assumed premiums written | 579,531 | 419,275
Assumed premiums earned | 244,306 | 123,271
Ceded premiums written | (1,353,214) | (1,164,406)
Ceded premiums earned | (983,549) | (827,126)
Net premiums written | 2 | (173)
Net premiums earned | $ 2 | $ (173)

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