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Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2024 | Mar. 31, 2023
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Favorable (adverse) development on prior years' loss reserves | $ 77,023 | $ 71,317
Reinsurance recoverable for retroactive reinsurance transaction | 0 | (125,067)
Insurance [Member] | International professional liability and marine and energy product lines [Member] |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Favorable (adverse) development on prior years' loss reserves | $ 64,800 |
Insurance [Member] | Marine and energy, property, workers' compensation and programs product lines [Member] |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Favorable (adverse) development on prior years' loss reserves |  | 63,800
Reinsurance [Member] |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Reinsurance recoverable for retroactive reinsurance transaction |  | $ (125,100)

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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