Investment Securities (Schedule Of Gross Unrealized Losses And Fair Values Of Securities) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Less than 12 months, Fair Value	$ 1,079,784	$ 1,821,091
Less than 12 months, Gross Unrealized Losses	(29,356)	(44,501)
12 months or more, Fair Value	131,588	170,536
12 months or more, Gross Unrealized Losses	(6,467)	(17,506)
Total, Fair Value	1,211,372	1,991,627
Total, Gross Unrealized Losses	(35,823)	(62,007)
Debt Securities [Member] | U.S. Treasury And Other U.S. Government Corporations And Agencies [Member] | U.S. Treasury And Agency Obligations [Member]
Less than 12 months, Fair Value	168,248	141,766
Less than 12 months, Gross Unrealized Losses	(480)	(615)
12 months or more, Fair Value	0	0
12 months or more, Gross Unrealized Losses	0	0
Total, Fair Value	168,248	141,766
Total, Gross Unrealized Losses	(480)	(615)
Debt Securities [Member] | U.S. Treasury And Other U.S. Government Corporations And Agencies [Member] | Mortgage-Backed Securities [Member]
Less than 12 months, Fair Value	23,462	110,358
Less than 12 months, Gross Unrealized Losses	(517)	(1,054)
12 months or more, Fair Value	19,428	5,557
12 months or more, Gross Unrealized Losses	(662)	(119)
Total, Fair Value	42,890	115,915
Total, Gross Unrealized Losses	(1,179)	(1,173)
Debt Securities [Member] | Tax-Exempt Municipal Securities [Member]
Less than 12 months, Fair Value	140,105	1,168,221
Less than 12 months, Gross Unrealized Losses	(1,634)	(33,218)
12 months or more, Fair Value	66,439	97,809
12 months or more, Gross Unrealized Losses	(2,025)	(10,401)
Total, Fair Value	206,544	1,266,030
Total, Gross Unrealized Losses	(3,659)	(43,619)
Debt Securities [Member] | Residential Mortgage-Backed Securities [Member]
Less than 12 months, Fair Value	4,911	0
Less than 12 months, Gross Unrealized Losses	(104)	0
12 months or more, Fair Value	25,560	32,671
12 months or more, Gross Unrealized Losses	(1,537)	(2,675)
Total, Fair Value	30,471	32,671
Total, Gross Unrealized Losses	(1,641)	(2,675)
Debt Securities [Member] | Commercial Mortgage-Backed Securities [Member]
Less than 12 months, Fair Value	42,559	0
Less than 12 months, Gross Unrealized Losses	(1,165)	0
12 months or more, Fair Value	0	2,752
12 months or more, Gross Unrealized Losses	0	(171)
Total, Fair Value	42,559	2,752
Total, Gross Unrealized Losses	(1,165)	(171)
Debt Securities [Member] | Asset-Backed Securities [Member]
Less than 12 months, Fair Value	18,932	17,069
Less than 12 months, Gross Unrealized Losses	(112)	(42)
12 months or more, Fair Value	3,656	283
12 months or more, Gross Unrealized Losses	(18)	(2)
Total, Fair Value	22,588	17,352
Total, Gross Unrealized Losses	(130)	(44)
Debt Securities [Member] | Corporate Debt Securities [Member]
Less than 12 months, Fair Value	681,567	383,677
Less than 12 months, Gross Unrealized Losses	(25,344)	(9,572)
12 months or more, Fair Value	16,505	31,464
12 months or more, Gross Unrealized Losses	(2,225)	(4,138)
Total, Fair Value	698,072	415,141
Total, Gross Unrealized Losses	$ (27,569)	$ (13,710)