Investment Securities (Schedule Of Contractual Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 16,913
Available-for-sale securities, after one year through five years, amortized cost	122,809
Available-for-sale securities, after five years through ten years, amortized cost	967,343
Available-for-sale securities, after ten years, amortized cost	2,578,585
Available-for-sale securities, amortized cost	3,685,650	$ 2,801,500
Available-for-sale securities, due within one year, fair value	17,150
Available-for-sale securities, after one year through five years, fair value	128,548
Available-for-sale securities, after five years through ten years, fair value	1,004,037
Available-for-sale securities, after ten years, fair value	2,573,436
Debt Securities, Available-for-sale	3,723,171	2,932,558
Held-to-maturity securities, due within one year, amortized cost	0
Held-to-maturity securities, after one year through five years, amortized cost	2
Held-to-maturity securities, after five years through ten years, amortized cost	8
Held-to-maturity securities, after ten years, amortized cost	2,785
Investment securities held to maturity	2,795	3,034
Held-to-maturity securities, due within one year, fair value	0
Held-to-maturity securities, after one year through five years, fair value	2
Held-to-maturity securities, after five years through ten years, fair value	8
Held-to-maturity securities, after ten years, fair value	3,571
Held-to-maturity securities, fair value	$ 3,581	$ 3,883