Investment Securities (Schedule Of Amortized Cost And Fair Value By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Marketable Securities [Abstract]
Held-to-maturity Securities, Debt Maturities, within 1 Year, Amortized Cost	$ 0
Held-to-maturity Securities, Debt Maturities, after 1 year; within 5 years, Amortized Cost	0
Held-to-maturity Securities, Debt Maturities, after 1 year; within 10 years, Amortized Cost	10,000
Held-to-maturity Securities, Debt Maturities, after 10 years, Amortized Cost	0
Held-to-maturity Securities, Debt Maturities, Subtotal, Amortized Cost	10,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount	0
Securities held to maturity, Amortized cost	10,000	$ 10,000
Held-to-maturity Securities, Debt Maturities, within 1 year, Fair Value	0
Held-to-maturity Securities, Debt Maturities, after 1 year; within 5 years, Fair Value	0
Held-to-maturity Securities, Debt Maturities, after 1 year; within 10 years, Fair Value	9,817
Held-to-maturity Securities, Debt Maturities, after 10 years, Fair Value	0
Held-to-maturity Securities, Debt Maturities, Subtotal, Fair Value	9,817
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	0
Held-to-maturity Securities, Fair Value	9,817	9,901
Within 1 year, Amortized Cost	0
After 1 year; within 5 years, Amortized Cost	85,638
After 5 years; within 10 years, Amortized Cost	512
After 10 years, Amortized Cost	0
Securities available for sale, Amortized Cost	86,150
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	4,852,026
Securities available for sale, Amortized Cost	4,938,176
Within 1 year, Fair Value	0
After 1 year; within 5 years, Fair Value	85,733
After 5 years; within 10 years, Fair Value	1,897
After 10 years, Fair Value	1,322
Subtotal, Fair Value	88,952
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	4,737,203
Securities available-for-sale	$ 4,826,155	$ 5,170,255