Derivative Financial Instruments - Effect on the Consolidated Statement of Comprehensive Income (Details) - Noninterest income - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Interest rate swaps
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	$ 58,976	$ 9,439
Mortgage loan commitments
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	(105)	(24)
Mortgage loan forward sale contracts
Derivative [Line Items]
Amount of Gain (Loss) Recognized in Income	$ 105	$ 24

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

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration