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	Dec. 31, 2020		Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Available-for-sale Securities, debt maturities, within one year, Amortized Cost	$ 143,462		$ 6,861
Available-for-sale Securities, debt maturities, after one year through three years, Amortized Cost	134,040		229,184
Available-for-sale Securities, debt maturities, after three year through five years, Amortized Cost	247,907		422,236
Available-for-sale Securities, debt maturities, after five through ten years, Amortized Cost	429,921		409,664
Available-for-sale Securities, debt maturities, after ten years, Amortized Cost	1,229,009		2,186,096
Available-for-sale Securities, debt maturities, Amortized Cost	2,184,339		3,254,041
Available-for-sale Securities, debt maturities, within one year, Fair Value	144,362	[1]	6,871
Available-for-sale Securities, debt maturities, after one year through three years, Fair Value	137,625		229,760
Available-for-sale Securities, debt maturities, after three year through five years, Fair Value	266,139		429,909
Available-for-sale Securities, debt maturities, after five through ten years, fair value	435,111	[1]	411,680
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	1,247,060	[1]	2,176,517
Available-for-sale Securities, debt maturities, Fair Value	2,230,297	[1]	3,254,737
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	1,932,439		598,250
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost	2,167,485		2,257,969
Held-to-maturity Securities, Amortized cost	4,117,384		2,856,219
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	1,926,425		597,166
Held-to-maturity Securities, debt maturities, after ten years, Fair Value	2,164,075		2,230,717
Held-to-maturity Securities, debt maturities, Fair Value	$ 4,107,960		$ 2,827,883

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