Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 24,236
Available-for-sale securities, after one year through five years, amortized cost	52,813
Available-for-sale securities, after five years through ten years, amortized cost	796,964
Available-for-sale securities, after ten years, amortized cost	1,929,275
Available-for-sale securities, amortized cost	2,803,288	$ 3,045,887
Available-for-sale securities, due within one year, fair value	24,228
Available-for-sale securities, after one year through five years, fair value	53,341
Available-for-sale securities, after five years through ten years, fair value	811,297
Available-for-sale securities, after ten years, fair value	1,953,210
Debt Securities, Available-for-sale	2,842,076	2,977,108
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	16
Held-to-maturity securities, after ten years, amortized cost	3,304
Investment securities held to maturity	3,320	3,606
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	16
Held-to-maturity securities, after ten years, fair value	4,322
Held-to-maturity securities, fair value	$ 4,338	$ 4,644