Investment Securities (Schedule Of Contractual Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 2,302
Available-for-sale securities, after one year through five years, amortized cost	94,866
Available-for-sale securities, after five years through ten years, amortized cost	431,773
Available-for-sale securities, after ten years, amortized cost	2,518,429
Available-for-sale securities, amortized cost	3,099,329
Available-for-sale securities, due within one year, fair value	2,313
Available-for-sale securities, after one year through five years, fair value	95,169
Available-for-sale securities, after five years through ten years, fair value	431,832
Available-for-sale securities, after ten years, fair value	2,484,485
Available-for-sale securities, fair value	3,065,769
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	19
Held-to-maturity securities, after ten years, amortized cost	3,784
Held to maturity, at amortized cost	3,803	$ 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	4,887
Held-to-maturity securities, fair value	4,906	$ 5,217
Other Investment Securities
Investment Holdings [Line Items]
Available-for-sale securities, amortized cost	51,959
Available-for-sale securities, fair value	51,970
Held to maturity, at amortized cost	0
Held-to-maturity securities, fair value	$ 0