Business Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Segment Reporting [Line Items]
Consolidated Assets	$ 45,677,113	$ 43,926,843
Operating Segments \| Insurance
Segment Reporting [Line Items]
Consolidated Assets	37,259,095	35,686,306
Operating Segments \| Reinsurance & Monoline Excess
Segment Reporting [Line Items]
Consolidated Assets	5,750,756	5,891,538
Corporate Reconciling Items And Eliminations
Segment Reporting [Line Items]
Consolidated Assets	$ 2,667,262	$ 2,348,999

Amount of asset recognized for present right to economic benefit.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details