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Segment Reporting Disclosures (Summary Of Deferred Policy Acquisition Costs, Unearned Premiums And Unpaid Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | --- | ---
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | $ 931,344 | $ 925,483 |  |
Unearned premiums | 6,642,426 | 6,220,748 |  |
Unpaid losses and loss adjustment expenses | 23,483,321 | 20,947,898 | $ 18,178,894 | $ 16,222,376
Underwriting Operations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 931,344 | 925,483 |  |
Unearned premiums | 5,216,330 | 4,946,266 |  |
Unpaid losses and loss adjustment expenses | 18,112,801 | 15,395,687 |  |
Market CATCo Re |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Unpaid losses and loss adjustment expenses | 184,967 | 347,921 |  |
Insurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 708,128 | 677,921 |  |
Unearned premiums | 4,307,704 | 4,015,252 |  |
Unpaid losses and loss adjustment expenses | 14,221,258 | 11,616,386 |  |
Reinsurance [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 223,216 | 247,562 |  |
Unearned premiums | 901,138 | 921,541 |  |
Unpaid losses and loss adjustment expenses | 3,726,472 | 3,581,699 |  |
Other underwriting [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 0 | 0 |  |
Unearned premiums | 7,488 | 9,473 |  |
Unpaid losses and loss adjustment expenses | 165,071 | 197,602 |  |
Program services and other fronting [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 0 | 0 |  |
Unearned premiums | 1,426,096 | 1,274,482 |  |
Unpaid losses and loss adjustment expenses | 5,185,553 | 5,204,290 |  |
Market CATCo Re |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Deferred policy acquisition costs | 0 | 0 |  |
Unearned premiums | 0 | 0 |  |
Unpaid losses and loss adjustment expenses | $ 184,967 | $ 347,921 |  |

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- Definition Amount of deferred policy acquisition cost capitalized on contract remaining in force. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 65 -Paragraph 2 -Subparagraph (g)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480016/944-40-65-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479432/944-30-50-2B Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479401/944-30-55-2 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(7)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 45 -Paragraph 1 -SubTopic 825 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479408/944-825-45-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 2B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479432/944-30-50-2B + Details
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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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