Industry Segments (Identifiable Assets by Segment) (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets		$ 22,230,934	$ 21,724,156	$ 21,716,691
Operating Segments [Member] | Reinsurance-Global Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets		2,595,231	2,441,340	2,713,554
Operating Segments [Member] | Insurance-Domestic Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets		18,232,365	18,063,730	17,944,847
Intersegment Eliminations and Corporate, Non-Segment [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Consolidated Assets	[1]	$ 1,403,338	$ 1,219,086	$ 1,058,290

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