Segment Reporting (Schedule Of Underwriting Results For Operating Segments To Income (Loss) Before Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting [Abstract]
Underwriting gain (loss)	$ 67,833	$ 7,213	$ 134,571	$ (193,438)
Net investment income	76,342	78,325	231,790	249,916
Net realized capital gains (losses)	95,943	(179,036)	354,673	(206,744)
Corporate expenses	(2,019)	(1,143)	(5,317)	(3,498)
Interest, fee and bond issue cost amortization expense	(12,682)	(12,706)	(38,061)	(38,083)
Other income (expense)	425	(8,865)	19,599	(20,401)
Income (loss) before taxes	$ 225,842	$ (116,212)	$ 697,255	$ (212,248)