Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands |
Jun. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Segment Reporting Information [Line Items] | ||
| Assets | $ 25,366,140 | $ 25,200,357 |
| Non-Insurance Operations [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Assets | 1,230,740 | 1,246,762 |
| Segment Assets [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Assets | 24,135,400 | 23,953,595 |
| Segment Assets [Member] | Investing [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Assets | 18,335,222 | 18,531,150 |
| Segment Assets [Member] | Underwriting [Member] | ||
| Segment Reporting Information [Line Items] | ||
| Assets | $ 5,800,178 | $ 5,422,445 |