Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 11,859,284	$ 11,532,103
Non-Insurance Operations [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	636,692	630,281
Segment Assets [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	11,222,592	10,901,822
Segment Assets [Member] | Investing [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	8,795,416	8,692,391
Segment Assets [Member] | Underwriting [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 2,427,176	$ 2,209,431