Investment Securities (Amortized Cost And Estimated Fair Value Of Investments In Debt Securities By Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value	$ 1,034,870	$ 820,645
Obligations Of States And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Due within one year, Amortized cost	1,068
Securities Available-for-Sale, Due within one year, Fair value	1,081
Securities Available-for-Sale, Due one through five years, Amortized cost	222
Securities Available-for-Sale, Due one through five years, Fair value	232
Securities Available-for-Sale, Total, Amortized cost	1,290
Securities Available-for-Sale, Total Fair value	1,313	2,660
Securities Held-to-Maturity, Due within one year, Amortized cost	570
Securities Held-to-Maturity, Due within one year, Fair value	571
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	0
Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value	0
Securities Held-to-Maturity, Total, Amortized cost	570
Securities Held-to-Maturity, Total, Fair value	571
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	695,633
Securities Available-for-Sale, Due within one year, Fair value	698,470
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	0
Securities Available-for-Sale, Due five through ten years, Fair value	0
Securities Available-for-Sale, Total, Amortized cost	695,633
Securities Available-for-Sale, Total Fair value	698,470	371,657
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total, Amortized cost	315,057
Securities Available-for-Sale, Total Fair value	332,848	444,295
Securities Held-to-Maturity, Total, Amortized cost	552,034
Securities Held-to-Maturity, Total, Fair value	$ 565,028