Industry Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 23,364,844	$ 21,730,967
Operating Segments | Insurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	19,137,758	18,063,730
Operating Segments | Reinsurance
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	2,524,338	2,441,340
Corporate, Other and Eliminations Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	$ 1,702,748	$ 1,225,897	[1]

[1] Corporate, other and eliminations represent corporate revenues and expenses and other items that are not allocated to business segments