Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 22,399
Available-for-sale securities, after one year through five years, amortized cost	73,780
Available-for-sale securities, after five years through ten years, amortized cost	435,437
Available-for-sale securities, after ten years, amortized cost	2,490,522
Available-for-sale securities, amortized cost	3,022,138
Available-for-sale securities, due within one year, fair value	22,267
Available-for-sale securities, after one year through five years, fair value	73,824
Available-for-sale securities, after five years through ten years, fair value	429,274
Available-for-sale securities, after ten years, fair value	2,422,049
Available-for-sale securities, fair value	2,947,414
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	18
Held-to-maturity securities, after ten years, amortized cost	3,649
Investment securities held to maturity	3,667	$ 3,803
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	19
Held-to-maturity securities, after ten years, fair value	4,650
Held-to-maturity securities, fair value	$ 4,669	$ 4,906