Securities (Carrying Value of Mortgage Backed Securities in Portfolio) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Sep. 30, 2011
FNMA [Member]
Schedule of Investments [Line Items]
Mortgage Backed Securities	$ 1,346,180	$ 1,384,396
FHLMC [Member]
Schedule of Investments [Line Items]
Mortgage Backed Securities	859,644	823,728
GNMA [Member]
Schedule of Investments [Line Items]
Mortgage Backed Securities	198,505	202,340
Private Issuer [Member]
Schedule of Investments [Line Items]
Mortgage Backed Securities	1,356	1,612
MBS [Member]
Schedule of Investments [Line Items]
Mortgage Backed Securities	$ 2,405,685	$ 2,412,076