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	Jun. 30, 2021		Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Available-for-sale Securities, debt maturities, within one year, Amortized Cost	$ 110,790		$ 143,462
Available-for-sale Securities, debt maturities, after one year through three years, Amortized Cost	200,105		134,040
Available-for-sale Securities, debt maturities, after three year through five years, Amortized Cost	155,783		247,907
Available-for-sale Securities, debt maturities, after five through ten years, Amortized Cost	454,812		429,921
Available-for-sale Securities, debt maturities, after ten years, Amortized Cost	1,320,137		1,229,009
Available-for-sale Securities, debt maturities, Amortized Cost	2,241,627		2,184,339
Available-for-sale Securities, debt maturities, within one year, Fair Value	111,102	[1]	144,362
Available-for-sale Securities, debt maturities, after one year through three years, Fair Value	206,467		137,625
Available-for-sale Securities, debt maturities, after three year through five years, Fair Value	165,832		266,139
Available-for-sale Securities, debt maturities, after five through ten years, fair value	462,396	[1]	435,111
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	1,334,360	[1]	1,247,060
Available-for-sale Securities, debt maturities, Fair Value	2,280,157	[1]	2,230,297
Held-to-maturity Securities, debt maturities, after three through five years, Amortized Cost			17,460
Held-to-maturity Securities, debt maturities, after five through ten years, Amortized Cost	2,127,088		1,932,439
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost	2,860,524		2,167,485
Held-to-maturity Securities, Amortized cost	4,987,612		4,117,384
Held-to-maturity Securities, debt maturities, after three through five years, Fair Value			17,460
Held-to-maturity Securities, debt maturities, after five through ten years, Fair Value	2,123,921		1,926,425
Held-to-maturity Securities, debt maturities, after ten years, Fair Value	2,868,218		2,164,075
Held-to-maturity Securities, debt maturities, Fair Value	$ 4,992,139		$ 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.