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BORROWINGS - Weighted Average Cost and Amount of Advances (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Debt Disclosure [Abstract] |  |  |
Weighted average interest rate, including cash flow hedges, at end of year | 2.35% | 3.32% | 3.83%
Weighted daily average interest rate, including cash flow hedges, during the year | 3.09% | 3.78% | 3.42%
Daily average of FHLB advances during the year | $ 2,260,209 | $ 2,952,872 | $ 2,916,849
Maximum amount of FHLB advances at any month end | 2,913,373 | 4,338,731 | 3,425,000
Interest expense during the year (including swap interest income and expense) | $ 69,912 | $ 111,574 | $ 99,631

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- Definition The calculated weighted average interest rate for Federal Home Loan Bank advances outstanding as of the Balance Sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(13)(3)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 + Details
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- Definition The calculated weighted average interest rate for Federal Home Loan Bank advances for the period ended as of the Balance Sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(13)(3)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 + Details
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