Investment Securities (Amortized Cost And Estimated Fair Value Of Investments In Debt Securities By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value	$ 1,046,910	$ 1,091,881
Securities Held-to-Maturity, Amortized Cost	347,622	357,197
Securities held-to-maturity, fair value	346,199	363,779
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	2,446
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	$ 2,420
Held to Maturity Securities weighted avg yield five through ten	2.97%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 297,409
Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value	$ 297,240
Held to Maturity Securities Debt Maturities Years Over Ten weighted avg yield	3.68%
Securities Held-to-Maturity, Amortized Cost	$ 299,855	300,412
Securities held-to-maturity, fair value	$ 299,660	306,274
Held to Maturity Securities weighted avg yield	3.67%
Obligations Of U.S. Treasury And Other U.S. Government Sponsored Entities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total Fair value		242,720
U.S. Government Sponsored Entities Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Securities Available-for-Sale, Total, Amortized cost	$ 1,079,745
Securities Available-for-Sale, Total Fair value	$ 1,046,910	849,161
Available for Sale Securities Weighted Avg Yield	2.28%
Securities Held-to-Maturity, Amortized Cost	$ 47,767	56,785
Securities held-to-maturity, fair value	$ 46,539	$ 57,505
Held to Maturity Securities weighted avg yield	2.83%