Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Available-for-sale securities, three months or less, amortized cost	$ 0
Available-for-sale securities, over three months through twelve months, amortized cost	1,904
Available-for-sale securities, after one year through five years, amortized cost	80,558
Available-for-sale securities, after five years through ten years, amortized cost	402,632
Available-for-sale securities, after ten years, amortized cost	2,787,047
Available-for-sale securities, amortized cost	3,274,100
Available-for-sale securities, three months or less, fair value	0
Available-for-sale securities, over three months through twelve months, fair value	1,922
Available-for-sale securities, after one year through five years, fair value	81,463
Available-for-sale securities, after five years through ten years, fair value	406,211
Available-for-sale securities, after ten years, fair value	2,751,842
Available-for-sale securities, fair value	3,243,408
Held-to-maturity securities, three months or less, amortized cost	1
Held-to-maturity securities, over three months through twelve months, 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	9
Held-to-maturity securities, after ten years, amortized cost	4,111
Investment securities held to maturity	4,121	$ 4,216
Held-to-maturity securities, three months or less, fair value	1
Held-to-maturity securities, over three months through twelve months, 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	10
Held-to-maturity securities, after ten years, fair value	5,135
Held-to-maturity securities, fair value	5,146	$ 5,217
Other Investment Securities
Investment Holdings [Line Items]
Available-for-sale securities, amortized cost	1,959
Available-for-sale securities, fair value	1,970
Investment securities held to maturity	0
Held-to-maturity securities, fair value	$ 0