Investment Securities (Amortized Cost And Estimated Fair Value Of Investments In Debt Securities By Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value	$ 1,007,481	$ 820,645
Obligations Of U.S. Treasury And Other U.S. Government Sponsored Entities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Due within one year, Amortized cost	249,125
Securities Available-for-Sale, Due within one year, Fair value	249,604
Securities Available-for-Sale, Due one through five years, Amortized cost	275,000
Securities Available-for-Sale, Due one through five years, Fair value	273,532
Securities Available-for-Sale, Due five through ten years, Amortized cost	75,000
Securities Available-for-Sale, Due five through ten years, Fair value	74,339
Securities Available-for-Sale, Total, Amortized cost	599,125
Securities Available-for-Sale, Total Fair value	597,475	371,657
Obligations Of States And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Due within one year, Amortized cost	2,121
Securities Available-for-Sale, Due within one year, Fair value	2,130
Securities Available-for-Sale, Due one through five years, Amortized cost	495
Securities Available-for-Sale, Due one through five years, Fair value	525
Securities Available-for-Sale, Total, Amortized cost	2,616
Securities Available-for-Sale, Total Fair value	2,655	2,660
Securities Held-to-Maturity, Due within one year, Amortized cost	1,427
Securities Held-to-Maturity, Due within one year, Fair value	1,430
Securities Held-to-Maturity, Total, Amortized cost	1,427
Securities Held-to-Maturity, Total, Fair value	1,430
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total, Amortized cost	388,444
Securities Available-for-Sale, Total Fair value	405,178	444,295
Securities Held-to-Maturity, Total, Amortized cost	780,823
Securities Held-to-Maturity, Total, Fair value	$ 793,645