Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Assets	$ 24,941,271	$ 25,200,357	$ 23,955,511
Non-Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	1,497,614	1,246,762	936,448
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	23,443,657	23,953,595	23,019,063
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	18,056,947	18,531,150	17,550,332
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,386,710	$ 5,422,445	$ 5,468,731