Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 1,414
Available-for-sale securities, after one year through five years, amortized cost	93,154
Available-for-sale securities, after five years through ten years, amortized cost	377,171
Available-for-sale securities, after ten years, amortized cost	2,458,549
Available-for-sale securities, amortized cost	2,930,288	$ 3,045,887
Available-for-sale securities, due within one year, fair value	1,426
Available-for-sale securities, after one year through five years, fair value	93,223
Available-for-sale securities, after five years through ten years, fair value	375,130
Available-for-sale securities, after ten years, fair value	2,424,999
Debt Securities, Available-for-sale	2,894,778	2,977,108
Held-to-maturity securities, due within one year, amortized cost	0
Held-to-maturity securities, after one year through five years, amortized cost	0
Held-to-maturity securities, after five years through ten years, amortized cost	14
Held-to-maturity securities, after ten years, amortized cost	3,464
Investment securities held to maturity	3,478	3,606
Held-to-maturity securities, due within one year, fair value	0
Held-to-maturity securities, after one year through five years, fair value	0
Held-to-maturity securities, after five years through ten years, fair value	14
Held-to-maturity securities, after ten years, fair value	4,503
Held-to-maturity securities, fair value	$ 4,517	$ 4,644