Investment Securities (Schedule Of Contractual Maturities Of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Available-for-sale securities, due within one year, amortized cost	$ 7,369
Available-for-sale securities, after one year through five years, amortized cost	85,999
Available-for-sale securities, after five years through ten years, amortized cost	892,947
Available-for-sale securities, after ten years, amortized cost	1,815,185
Available-for-sale securities, amortized cost	2,801,500	$ 2,790,248
Available-for-sale securities, due within one year, fair value	7,441
Available-for-sale securities, after one year through five years, fair value	89,172
Available-for-sale securities, after five years through ten years, fair value	963,994
Available-for-sale securities, after ten years, fair value	1,871,951
Available-for-sale securities, fair value	2,932,558	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	3,021
Held to maturity, at amortized cost	3,034	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	3,870
Held-to-maturity securities, fair value	$ 3,883	$ 4,263