Segment Reporting (Schedule Of Underwriting Results For Operating Segments To Income (Loss) Before Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting [Abstract]
Underwriting gain (loss)									$ 42,851	$ (576,734)	$ (138,520)
Net investment income	74,355	76,342	74,206	81,242	63,017	78,325	84,459	87,132	306,145	312,933	350,344
Net realized capital gains (losses)	37,029	95,943	82,589	176,141	165,628	(179,036)	(68,184)	40,476	391,702	(41,116)	65,291
Corporate expenses									(8,764)	(6,073)	(5,867)
Interest, fee and bond issue cost amortization expense									(50,746)	(50,763)	(54,553)
Other income (expense)									12,136	(11,745)	12,074
Income (loss) before taxes									$ 693,324	$ (373,498)	$ 228,769