Available-For-Sale And Held-To-Maturity Securities (Schedule Of Amortized Cost And Fair Values Of Debt Securities By Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2021		Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-sale Securities, debt maturities, within one year, Amortized Cost	$ 133,899		$ 143,462
Available-for-sale Securities, debt maturities, after one year through three years, Amortized Cost	121,840		134,040
Available-for-sale Securities, debt maturities, after three year through five years, Amortized Cost	242,071		247,907
Available-for-sale Securities, debt maturities, after five through ten years, Amortized Cost	348,662		429,921
Available-for-sale Securities, debt maturities, after ten years, Amortized Cost	1,319,527		1,229,009
Available-for-sale Securities, debt maturities, Amortized Cost	2,165,999		2,184,339
Available-for-sale Securities, debt maturities, within one year, Fair Value	134,463	[1]	144,362
Available-for-sale Securities, debt maturities, after one year through three years, Fair Value	124,825		137,625
Available-for-sale Securities, debt maturities, after three year through five years, Fair Value	254,774		266,139
Available-for-sale Securities, debt maturities, after five through ten years, fair value	350,871	[1]	435,111
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	1,325,195	[1]	1,247,060
Available-for-sale Securities, debt maturities, Fair Value	2,190,128	[1]	2,230,297
Held-to-maturity Securities, debt maturities, after three through five years, Amortized Cost	1,623		17,460
Held-to-maturity Securities, debt maturities, after five through ten years, Amortized Cost	2,157,703		1,932,439
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost	2,602,075		2,167,485
Held-to-maturity Securities, Amortized cost	4,761,401		4,117,384
Held-to-maturity Securities, debt maturities, after three through five years, Fair Value	1,623		17,460
Held-to-maturity Securities, debt maturities, after five through ten years, Fair Value	2,155,117		1,926,425
Held-to-maturity Securities, debt maturities, after ten years, Fair Value	2,608,284		2,164,075
Held-to-maturity Securities, debt maturities, Fair Value	$ 4,765,024		$ 4,107,960

[1] Due to the immaterial amount of income recognized on tax-exempt securities, yields were not calculated on a tax-equivalent basis.