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Borrowings - Narrative (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items] |  |
Borrowings | $ 3,267,589,000 | $ 3,650,000,000
Weighted average effective maturity of FHLB advances | 2 years 4 months 2 days |
FRB Bank Term Funding Program |  |
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items] |  |
Issued amount | $ 325,000,000 | $ 750,000,000
Debt term | 1 year |
Federal Home Loan Bank of Des Moines |  |
Federal Home Loan Bank, Advance, Branch of FHLBank [Line Items] |  |
Federal home loan bank, percent of assets | 45.00% |

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