Securities Sold Under Agreements to Repurchase - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
Jun. 30, 2017	Sep. 30, 2016
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase	$ 128.2	$ 151.8
Securities sold under agreements to repurchase, fair value of collateral	$ 126.4	$ 152.3
Securities sold under agreements to repurchase, collateral, percentage of borrowed funds (as a percent)	102.00%

Amount, before effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226000-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Repurchase Agreement Accounted for as a Collateralized Borrowing
-URI http://asc.fasb.org/extlink&oid=49203159

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant