Fair Values (Schedule Of Fair Value Assets And Liabilities Measured On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009	Dec. 31, 2008
Trading securities	$ 2,309		$ 3,024
Available for sale securities	3,168,578		2,919,180
Mortgage servicing rights, at fair value	18,184		14,454		12,625	8,205
Derivatives	7,955		1,060
Total assets measured at fair value	3,197,026		2,937,718
Junior subordinated debentures, at fair value	82,905		80,688
Derivatives	6,509		361
Total liabilities measured at fair value	89,414		81,049
Level 1 [Member]
Total assets measured at fair value	2,309		3,024
Level 2 [Member]
Derivatives	7,955		1,060
Total assets measured at fair value	3,176,533		2,920,240
Derivatives	6,509		361
Total liabilities measured at fair value	6,509		361
Level 3 [Member]
Mortgage servicing rights, at fair value	18,184		14,454
Total assets measured at fair value	18,184		14,454
Junior subordinated debentures, at fair value	82,905		80,688
Total liabilities measured at fair value	82,905		80,688
Obligations Of States And Political Subdivisions [Member]
Trading securities	296		1,282
Available for sale securities	253,553		216,726
Obligations Of States And Political Subdivisions [Member] | Level 1 [Member]
Trading securities	296		1,282
Obligations Of States And Political Subdivisions [Member] | Level 2 [Member]
Available for sale securities	253,553		216,726
Equity Securities [Member]
Trading securities	1,918		1,645
Equity Securities [Member] | Level 1 [Member]
Trading securities	1,918		1,645
Other Investments Securities [Member]
Trading securities	95	[1]	97	[1]
Other Investments Securities [Member] | Level 1 [Member]
Trading securities	95	[1]	97	[1]
U.S. Treasury And Agencies [Member]
Available for sale securities	118,465		118,789
U.S. Treasury And Agencies [Member] | Level 2 [Member]
Available for sale securities	118,465		118,789
Residential Mortgage-Backed Securities And Collateralized Mortgage Obligations [Member]
Available for sale securities	2,794,355		2,581,504
Residential Mortgage-Backed Securities And Collateralized Mortgage Obligations [Member] | Level 2 [Member]
Available for sale securities	2,794,355		2,581,504
Other Debt Securities [Member]
Available for sale securities	134		152
Other Debt Securities [Member] | Level 2 [Member]
Available for sale securities	134		152
Investments In Mutual Funds And Other Equity Securities [Member]
Available for sale securities	2,071		2,009
Investments In Mutual Funds And Other Equity Securities [Member] | Level 2 [Member]
Available for sale securities	$ 2,071		$ 2,009

[1] Principally represents U.S. Treasury and agencies or residential mortgage-backed securities issued or guaranteed by governmental agencies.