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Derivatives and Hedging Activities - Impact of Client Swap Program that are Not Designated in Accounting Hedges (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2020 | Sep. 30, 2019
Client swap program hedges |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 0 | $ 0
Other noninterest income | Pay fixed/receive floating swap |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | (27,820) | (33,112)
Other noninterest income | Receive fixed/pay floating swap |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 27,820 | $ 33,112

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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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4CC -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109998890-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121590274&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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