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Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details) - Cash flow hedging - USD ($) $ in Thousands | 3 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Derivative [Line Items] |  |
Total pre-tax gain/(loss) recognized in AOCI | $ 21,599 | $ (40,527)
Pay fixed/receive floating swaps on borrowings cash flow hedges |  |
Derivative [Line Items] |  |
Pay fixed/receive floating swaps on borrowings cash flow hedges | 21,594 | (40,527)
Reclassification adjustment of net (gain)/loss included in net income | $ 5 | $ 0

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