Investment Securities (Schedule Of Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 3,264
Available-for-sale securities, after one year through five years, amortized cost	71,383
Available-for-sale securities, after five years through ten years, amortized cost	904,677
Available-for-sale securities, after ten years, amortized cost	1,779,805
Available-for-sale securities, amortized cost	2,759,129	$ 2,790,248
Available-for-sale securities, due within one year, fair value	3,298
Available-for-sale securities, after one year through five years, fair value	73,499
Available-for-sale securities, after five years through ten years, fair value	979,854
Available-for-sale securities, after ten years, fair value	1,842,049
Debt Securities, Available-for-sale	2,898,700	2,814,682
Held-to-maturity securities, due within one year, amortized cost	0
Held-to-maturity securities, after one year through five years, amortized cost	3
Held-to-maturity securities, after five years through ten years, amortized cost	10
Held-to-maturity securities, after ten years, amortized cost	3,075
Investment securities held to maturity	3,088	3,260
Held-to-maturity securities, due within one year, fair value	0
Held-to-maturity securities, after one year through five years, fair value	3
Held-to-maturity securities, after five years through ten years, fair value	10
Held-to-maturity securities, after ten years, fair value	3,937
Held-to-maturity securities, fair value	$ 3,950	$ 4,263