Investment Securities (Amortized Cost And Estimated Fair Value Of Investments In Debt Securities By Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value	$ 867,147	$ 820,645
Obligations Of States And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Due within one year, Amortized cost	2,120
Securities Available-for-Sale, Due within one year, Fair value	2,131
Securities Available-for-Sale, Due one through five years, Amortized cost	495
Securities Available-for-Sale, Due one through five years, Fair value	519
Securities Available-for-Sale, Total, Amortized cost	2,615
Securities Available-for-Sale, Total Fair value	2,650	2,660
Securities Held-to-Maturity, Due within one year, Amortized cost	1,037
Securities Held-to-Maturity, Due within one year, Fair value	1,040
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	90
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	90
Securities Held-to-Maturity, Total, Amortized cost	1,127
Securities Held-to-Maturity, Total, Fair value	1,130
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	400,000
Securities Available-for-Sale, Due within one year, Fair value	401,961
Securities Available-for-Sale, Due one through five years, Amortized cost	0
Securities Available-for-Sale, Due one through five years, Fair value	0
Securities Available-for-Sale, Due five through ten years, Amortized cost	90,000
Securities Available-for-Sale, Due five through ten years, Fair value	89,808
Securities Available-for-Sale, Total, Amortized cost	490,000
Securities Available-for-Sale, Total Fair value	491,769	371,657
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total, Amortized cost	352,970
Securities Available-for-Sale, Total Fair value	370,592	444,295
Securities Held-to-Maturity, Total, Amortized cost	754,095
Securities Held-to-Maturity, Total, Fair value	$ 766,946