Securities (Amortized Cost, Estimated Fair Value, and Gross Unrealized Gains and Losses of AFS and HTM Securities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 845,958	$ 1,058,283
Available-for-sale Securities, Gross Unrealized Gains	16,458	19,741
Available-for-sale Securities, Gross Unrealized Losses	5,044	8,057
Available-for-sale Securities, Estimated Fair Value	857,372	1,069,967
Held-to-maturity Securities, Amortized Cost	1,637,043	1,718,023
Held-to-maturity Securities, Gross Unrealized Gains	37,222	40,821
Held-to-maturity Securities, Gross Unrealized Losses	10,348	16,998
Held-to-maturity securities, Estimated Fair Value	1,663,917	1,741,846
Marketable Securities, Amortized Cost	2,483,001	2,776,306
Marketable Securities, Gross Unrealized Gains	53,680	60,562
Marketable Securities, Gross Unrealized Losses	15,392	25,055
Marketable Securities, Estimated Fair Value	2,521,289	2,811,813
GSE Debentures [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost	554,821	709,118
Available-for-sale Securities, Gross Unrealized Gains	439	996
Available-for-sale Securities, Gross Unrealized Losses	4,829	7,886
Available-for-sale Securities, Estimated Fair Value	550,431	702,228
MBS [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost	287,496	345,263
Available-for-sale Securities, Gross Unrealized Gains	15,994	18,701
Available-for-sale Securities, Gross Unrealized Losses	47
Available-for-sale Securities, Estimated Fair Value	303,443	363,964
Held-to-maturity Securities, Amortized Cost	1,600,567	1,683,744
Held-to-maturity Securities, Gross Unrealized Gains	36,503	39,878
Held-to-maturity Securities, Gross Unrealized Losses	10,332	16,984
Held-to-maturity securities, Estimated Fair Value	1,626,738	1,706,638
Trust Preferred Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost	2,524	2,594
Available-for-sale Securities, Gross Unrealized Losses	168	171
Available-for-sale Securities, Estimated Fair Value	2,356	2,423
Municipal Bonds [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost	1,117	1,308
Available-for-sale Securities, Gross Unrealized Gains	25	44
Available-for-sale Securities, Estimated Fair Value	1,142	1,352
Held-to-maturity Securities, Amortized Cost	36,476	34,279
Held-to-maturity Securities, Gross Unrealized Gains	719	943
Held-to-maturity Securities, Gross Unrealized Losses	16	14
Held-to-maturity securities, Estimated Fair Value	$ 37,179	$ 35,208