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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, 2024 | Mar. 31, 2023
Effects of Reinsurance [Line Items] |  |
Direct premiums written | $ 2,852,425 | $ 2,542,574
Direct premiums earned | 2,901,920 | 2,612,989
Assumed premiums written | 1,087,974 | 893,438
Assumed premiums earned | 516,213 | 473,436
Ceded premiums written | (1,708,362) | (1,218,234)
Ceded premiums earned | (1,290,506) | (1,118,721)
Net premiums written | 2,232,037 | 2,217,778
Net premiums earned | 2,127,627 | 1,967,704
Underwriting [Member] |  |
Effects of Reinsurance [Line Items] |  |
Direct premiums written | 2,107,467 | 1,969,363
Direct premiums earned | 2,198,238 | 1,971,876
Assumed premiums written | 668,699 | 688,895
Assumed premiums earned | 392,942 | 398,719
Ceded premiums written | (543,956) | (440,029)
Ceded premiums earned | (463,380) | (402,440)
Net premiums written | 2,232,210 | 2,218,229
Net premiums earned | 2,127,800 | 1,968,155
Program services and other fronting [Member] |  |
Effects of Reinsurance [Line Items] |  |
Direct premiums written | 744,958 | 573,211
Direct premiums earned | 703,682 | 641,113
Assumed premiums written | 419,275 | 204,543
Assumed premiums earned | 123,271 | 74,717
Ceded premiums written | (1,164,406) | (778,205)
Ceded premiums earned | (827,126) | (716,281)
Net premiums written | (173) | (451)
Net premiums earned | $ (173) | $ (451)

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