Available-For-Sale And Held-To-Maturity Securities (Contractual Maturities) (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, within one year, Fair Value	[1]	$ 186,128
Available-for-sale Securities, debt maturities, after one year through five, Fair Value	[1]	586,778
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 one year through five, Amortized Cost		58,698
Held-to-maturity Securities, debt maturities, after five year through ten, 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
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, within one year, Fair Value	[1]	1,172
Available-for-sale Securities, debt maturities, after one year through five, Fair Value	[1]	3,854
Available-for-sale Securities, debt maturities, Fair Value	[1]	5,026
State And Municipal Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, within one year, Fair Value	[1]	359
Available-for-sale Securities, debt maturities, after five through ten years, fair value	[1]	18,559
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	50,947
Available-for-sale Securities, debt maturities, Fair Value	[1]	69,865
Corporate Fixed Income Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, within one year, Fair Value	[1]	184,597
Available-for-sale Securities, debt maturities, after one year through five, Fair Value	[1]	582,924
Available-for-sale Securities, debt maturities, after five through ten years, fair value	[1]	513,574
Available-for-sale Securities, debt maturities, Fair Value	[1]	1,281,095
Asset-Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, after five through ten years, fair value	[1]	362,525
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	1,638,697
Available-for-sale Securities, debt maturities, Fair Value	[1]	2,001,222
Held-to-maturity Securities, debt maturities, after five year through ten, Amortized Cost		571,991
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		1,933,056
Held-to-maturity Securities, Amortized cost		2,505,047
Mortgage Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
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 five year through ten, Amortized Cost		134,529
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		1,148,252
Mortgage Backed Securities [Member] | Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, debt maturities, after five through ten years, fair value	[1]	307
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	283,396
Available-for-sale Securities, debt maturities, Fair Value	[1]	283,703
Held-to-maturity Securities, debt maturities, after five year through ten, Amortized Cost		134,529
Held-to-maturity Securities, debt maturities, after ten years, Amortized Cost		1,148,252
Held-to-maturity Securities, Amortized cost	[2]	1,282,781	1,334,833
Mortgage Backed Securities [Member] | Commercial [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	70,449
Available-for-sale Securities, debt maturities, Fair Value	[1]	70,449
Held-to-maturity Securities, debt maturities, after one year through five, Amortized Cost		58,698
Held-to-maturity Securities, Amortized cost	[2]	58,698	$ 58,971
Mortgage Backed Securities [Member] | Non-Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Availably-for-sale Securities, debt maturities, after ten years, Fair Value	[1]	1,441
Available-for-sale Securities, debt maturities, Fair Value	[1]	$ 1,441

[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.