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Derivatives and Hedging Activities - Impact of Client Swap Program that are Not Designated in Accounting Hedges (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021
Client swap program hedges |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 0 | $ 0 | $ 0 | $ 0
Other noninterest income | Pay fixed/receive floating swap |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | 15,865 | 10,814 | 54,202 | 64,119
Other noninterest income | Receive fixed/pay floating swap |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ (15,865) | $ (10,814) | $ (54,202) | $ (64,119)

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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 https://asc.fasb.org/extlink&oid=125515794&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 https://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959 + Details
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