Derivative Financial Instruments - Effect on the Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Termination value of net liability position	$ 84,400	$ 53,500
Collateral posted	106,100	63,200
Noninterest income \| Interest rate swaps
Derivative [Line Items]
Amount of gain (loss) recognized in income	(48,658)	(62,088)	$ (30,177)
Noninterest income \| Mortgage loan commitments
Derivative [Line Items]
Amount of gain (loss) recognized in income	66	95	19
Noninterest income \| Mortgage loan forward sale contracts
Derivative [Line Items]
Amount of gain (loss) recognized in income	$ (66)	$ (95)	$ (19)

Derivative, Net Liability Position, Termination Value

No definition available.

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624258-113959

+ Details

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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