Securities (Carrying Value of Mortgage Backed Securities in Portfolio) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013
Schedule of Investments [Line Items]
Mortgage-backed securities	$ 1,904,010	$ 2,047,708
FNMA [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	1,108,947	1,250,948
FHLMC [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	632,224	629,216
GNMA [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities	$ 162,839	$ 167,544