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Derivatives and Hedging Activities (Details) - USD ($)	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Derivative [Line Items]
Gain (loss) on derivative instruments	$ 0	$ 0
Derivative asset, fair value	26,162,000		$ 1,139,000
Derivative liability, fair value	8,617,000		3,006,000
Interest rate swap agreements
Derivative [Line Items]
Customer derivatives program	808,981,000		1,035,573,000
Notional amount	700,000,000	$ 700,000,000
Commercial loan interest rate swap
Derivative [Line Items]
Notional amount	97,927,000		52,936,000
Interest rate contracts | Other assets
Derivative [Line Items]
Derivative asset, fair value	8,617,000		1,139,000
Interest rate contracts | Other liabilities
Derivative [Line Items]
Derivative liability, fair value	8,617,000		1,139,000
Commercial loan hedges | Other assets
Derivative [Line Items]
Derivative asset, fair value	2,217,000		0
Commercial loan hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value	0		174,000
Borrowings hedges | Other assets
Derivative [Line Items]
Derivative asset, fair value	15,328,000		0
Borrowings hedges | Other liabilities
Derivative [Line Items]
Derivative liability, fair value	$ 0		$ 1,693,000

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
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-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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