Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 22,299
Available-for-sale securities, after one year through five years, amortized cost	71,828
Available-for-sale securities, after five years through ten years, amortized cost	437,062
Available-for-sale securities, after ten years, amortized cost	2,403,000
Available-for-sale securities, amortized cost	2,934,189
Available-for-sale securities, due within one year, fair value	22,187
Available-for-sale securities, after one year through five years, fair value	71,743
Available-for-sale securities, after five years through ten years, fair value	430,012
Available-for-sale securities, after ten years, fair value	2,330,456
Available-for-sale securities, fair value	2,854,398
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	17
Held-to-maturity securities, after ten years, amortized cost	3,569
Investment securities held to maturity	3,586	$ 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	18
Held-to-maturity securities, after ten years, fair value	4,606
Held-to-maturity securities, fair value	$ 4,624	$ 4,906