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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
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Dec. 31, 2024 | Dec. 31, 2023
Client swap program hedges |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ 5 | $ 109
Other noninterest income | Pay fixed/receive floating swap |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | 20,185 | (28,709)
Other noninterest income | Receive fixed/pay floating swap |  |
Derivative [Line Items] |  |
Derivative instruments not designated as hedging instruments, gain (loss), net | $ (20,180) | $ 28,818

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