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Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details) - Cash flow hedging - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Derivative [Line Items] |  |  |  |
Total pre-tax gain/(loss) recognized in AOCI | $ (3,256) | $ 14,757 | $ (33,040) | $ (14,021)
Pay fixed/receive floating swaps on borrowings cash flow hedges |  |  |  |
Derivative [Line Items] |  |  |  |
Pay fixed/receive floating swaps on borrowings cash flow hedges | $ (3,256) | $ 14,757 | $ (33,040) | $ (14,021)

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