Business Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 33,076,819	$ 32,047,876
Operating Segments | Insurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	26,267,446	24,403,918
Operating Segments | Reinsurance & Monoline Excess
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	5,012,394	4,917,985
Corporate, other and eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 1,796,979	$ 2,725,973