Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 1,786
Available-for-sale securities, after one year through five years, amortized cost	101,898
Available-for-sale securities, after five years through ten years, amortized cost	416,627
Available-for-sale securities, after ten years, amortized cost	2,537,368
Available-for-sale securities, amortized cost	3,059,638
Available-for-sale securities, due within one year, fair value	1,791
Available-for-sale securities, after one year through five years, fair value	102,915
Available-for-sale securities, after five years through ten years, fair value	419,502
Available-for-sale securities, after ten years, fair value	2,521,167
Available-for-sale securities, fair value	3,047,358
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	3,887
Investment securities held to maturity	3,905	$ 4,216
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	5,000
Held-to-maturity securities, fair value	5,019	$ 5,217
Other Investment Securities
Investment Holdings [Line Items]
Available-for-sale securities, amortized cost	1,959
Available-for-sale securities, fair value	1,983
Investment securities held to maturity	0
Held-to-maturity securities, fair value	$ 0