Parent Company Information (Schedule Of Condensed Statements Of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Gains on securities transactions, net	$ 12,034	$ 863	$ 16,492	$ 2,679	$ 6,967	$ 112	$ 3,656	$ 863	$ 32,068	$ 11,598	$ 8,005
Trading gains (losses), net	(839)	776	(1,048)	3,382	(2,078)	(2,627)	838	(3,030)	2,271	(6,897)	(10,434)
Net impairment losses on securities recognized in earnings	19,143			825			2,049	2,593	(19,968)	(4,642)	(6,352)
Income tax benefit	7,528	13,696	25,205	17,103	15,322	14,168	14,081	12,200	63,532	55,771	51,484
Net Income	24,817	35,357	36,894	36,585	38,158	32,639	33,010	27,363	133,653	131,170	116,061
Dividends on preferred stock and accretion											19,524
Net Income Available to Common Stockholders									133,653	131,170	96,537
Parent Company [Member]
Dividends from subsidiary									115,000	65,000	120,000
Income from subsidiary									180	332	2,069
Gains on securities transactions, net										106
Trading gains (losses), net									1,256	(5,841)	(15,828)
Net impairment losses on securities recognized in earnings											(434)
Other interest and dividends									223	830	437
Total Income									116,659	60,427	106,244
Total Expenses									16,481	16,388	16,267
Income before income tax benefit and equity in undistributed earnings of subsidiary									100,178	44,039	89,977
Income tax benefit									(5,202)	(7,365)	(10,541)
Income before equity in undistributed earnings of subsidiary									105,380	51,404	100,518
Equity in undistributed earnings of subsidiary									28,273	79,766	15,543
Net Income									133,653	131,170	116,061
Dividends on preferred stock and accretion											19,524
Net Income Available to Common Stockholders									$ 133,653	$ 131,170	$ 96,537