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Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Effects of Reinsurance [Line Items] |  |  |
Direct premiums written | $ 12,094,040 | $ 11,306,483 | $ 10,729,950
Direct premiums earned | 11,855,424 | 10,999,889 | 10,068,570
Assumed premiums written | 3,400,591 | 2,695,754 | 2,471,732
Assumed premiums earned | 3,188,007 | 2,554,030 | 2,246,805
Ceded premiums written | (7,198,456) | (5,604,662) | (4,998,292)
Ceded premiums earned | (6,611,019) | (5,258,440) | (4,727,583)
Net premiums written | 8,296,175 | 8,397,575 | 8,203,390
Net premiums earned | 8,432,412 | 8,295,479 | 7,587,792
Underwriting [Member] |  |  |
Effects of Reinsurance [Line Items] |  |  |
Direct premiums written | 8,860,015 | 8,657,266 | 8,085,812
Direct premiums earned | 8,801,477 | 8,363,710 | 7,379,766
Assumed premiums written | 1,691,858 | 1,620,366 | 1,761,726
Assumed premiums earned | 1,628,408 | 1,616,630 | 1,589,920
Ceded premiums written | (2,252,122) | (1,878,844) | (1,640,165)
Ceded premiums earned | (1,993,895) | (1,683,648) | (1,378,191)
Net premiums written | 8,299,751 | 8,398,788 | 8,207,373
Net premiums earned | 8,435,990 | 8,296,692 | 7,591,495
Fronting [Member] |  |  |
Effects of Reinsurance [Line Items] |  |  |
Direct premiums written | 3,234,025 | 2,649,217 | 2,644,138
Direct premiums earned | 3,053,947 | 2,636,179 | 2,688,804
Assumed premiums written | 1,708,733 | 1,075,388 | 710,006
Assumed premiums earned | 1,559,599 | 937,400 | 656,885
Ceded premiums written | (4,946,334) | (3,725,818) | (3,358,127)
Ceded premiums earned | (4,617,124) | (3,574,792) | (3,349,392)
Net premiums written | (3,576) | (1,213) | (3,983)
Net premiums earned | $ (3,578) | $ (1,213) | $ (3,703)

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