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Reinsurance Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Losses) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Effects of Reinsurance [Line Items] |  |  |  |
Net losses and loss adjustment expenses | $ 1,290,612 | $ 1,404,325 | $ 3,810,934 | $ 3,765,215
Underwriting [Member] |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Gross losses and loss adjustment expenses | 1,710,637 | 1,684,389 | 4,982,304 | 4,552,926
Ceded losses and loss adjustment expenses | (419,194) | (278,945) | (1,170,585) | (786,876)
Net losses and loss adjustment expenses | $ 1,291,443 | $ 1,405,444 | $ 3,811,719 | $ 3,766,050

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- Definition Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(5)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 + Details
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