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Reinsurance Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Losses) (Details) - Underwriting [Member] - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Effects of Reinsurance [Line Items] |  |  |  |
Gross losses and loss adjustment expenses | $ 1,476,189 | $ 1,186,691 | $ 2,868,537 | $ 2,337,040
Ceded losses and loss adjustment expenses | (288,676) | (127,895) | (507,931) | (305,889)
Net losses and loss adjustment expenses | $ 1,187,513 | $ 1,058,796 | $ 2,360,606 | $ 2,031,151

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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//1943274/2147483586/944-220-S99-1 + Details
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