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, 2018	Dec. 31, 2017
Schedule Of Debt Securities At Amortized Cost And Fair Value Basis [Line Items]
Available-for-sale Securities, debt maturities, Amortized Cost		$ 3,734,922
Available-for-sale Securities, debt maturities, within one year, Fair Value	[1]	186,128
Available-for-sale Securities, debt maturities, after five through ten years, fair value	[1]	894,965
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	2,044,930
Available-for-sale Securities, debt maturities, Fair Value	[1]	3,712,801
Held-to-maturity Securities, debt maturities, after five through ten years, Amortized Cost		706,520
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		3,081,308
Held-to-maturity Securities, Amortized cost	[2]	3,846,526	$ 3,698,098
Held-to-maturity Securities, debt maturities, Fair Value	[2]	3,825,399	$ 3,710,478
Excluding Mortgage Backed Securities [Member]
Schedule Of Debt Securities At Amortized Cost And Fair Value Basis [Line Items]
Available-for-sale Securities, debt maturities, within one year, Amortized Cost		186,449
Available-for-sale Securities, debt maturities, after one year through three years, Amortized Cost		318,811
Available-for-sale Securities, debt maturities, after three year through five years, Amortized Cost		280,569
Available-for-sale Securities, debt maturities, after five through ten years, Amortized Cost		903,515
Availably-for-sale Securities, debt maturities, after ten years, Amortized Cost		1,680,244
Available-for-sale Securities, debt maturities, within one year, Fair Value		186,128
Available-for-sale Securities, debt maturities, after one year through three years, Fair Value		313,695
Available-for-sale Securities, debt maturities, after three year through five years, Fair Value		273,083
Available-for-sale Securities, debt maturities, after five through ten years, fair value		894,658
Availably-for-sale Securities, debt maturities, after ten years, Fair Value		1,689,644
Held-to-maturity Securities, debt maturities, after five through ten years, Amortized Cost		571,991
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		1,933,056
Held-to-maturity Securities, debt maturities, after five through ten years, Fair Value		574,299
Held-to-maturity Securities, debt maturities, after ten years, Fair Value		1,938,971
Mortgage Backed Securities [Member]
Schedule Of Debt Securities At Amortized Cost And Fair Value Basis [Line Items]
Available-for-sale Securities, debt maturities, after five through ten years, Amortized Cost		306
Availably-for-sale Securities, debt maturities, after ten years, Amortized Cost		365,028
Available-for-sale Securities, debt maturities, after five through ten years, fair value		307
Availably-for-sale Securities, debt maturities, after ten years, Fair Value		355,286
Held-to-maturity Securities, debt maturities, after three year through five years, Amortized Cost		58,698
Held-to-maturity Securities, debt maturities, after five through ten years, Amortized Cost		134,529
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		1,148,252
Held-to-maturity Securities, debt maturities, after three year through five years, Fair Value		58,895
Held-to-maturity Securities, debt maturities, after five through ten years, Fair Value		130,499
Held-to-maturity Securities, debt maturities, after ten years, Fair Value		$ 1,122,735

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

[2] Held-to-maturity securities are carried in the consolidated statements of financial condition at amortized cost, and the changes in the value of these securities, other than impairment charges, are not reported on the consolidated financial statements.