Securities (Carrying Value of Mortgage Backed Securities in Portfolio) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013
Schedule of Investments [Line Items]
Mortgage-backed securities	$ 1,975,164	$ 2,047,708
FNMA [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	1,193,334	1,250,948
FHLMC [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	622,975	629,216
GNMA [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	$ 158,855	$ 167,544