Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Assets	$ 26,335,628	$ 24,939,115
Non-Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	1,536,669	1,497,042
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	24,798,959	23,442,073
Segment Assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	18,976,263	18,056,947
Segment Assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,822,696	$ 5,385,126