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Business Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 43,715,217	$ 40,448,635
Operating Segments | Insurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	35,721,098	32,911,507
Operating Segments | Reinsurance & Monoline Excess
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	6,015,394	5,669,729
Corporate Reconciling Items And Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 1,978,725	$ 1,867,399

X

- Definition

Amount of asset recognized for present right to economic benefit.

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