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DERIVATIVES AND HEDGING ACTIVITIES - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details) - USD ($) | 12 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024
Derivatives, Fair Value [Line Items] |  |
Carrying value of hedged items | $ 6,366,196,000 | $ 7,287,540,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration] |  | Loans receivable, net of allowance for loan losses of $199,720 and $203,753
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | 22,246,000 | $ 20,005,000
Mortgage loan fair value hedges |  |
Derivatives, Fair Value [Line Items] |  |
Portfolio layer method, amortized cost | 5,393,257,000 | 7,252,017,000
Portfolio layer method, cumulative adjustment, increase (decrease) | 8,262,000 | 21,476,000
Amortized cost, designated in portfolio hedging relationship | 1,570,000,000 | 2,570,000,000
Hedged asset, discontinued | 1,600,000,000 | 300,000,000
Hedged asset, discontinued fair value | 4,016,668 | 1,232,211
Commercial loan fair value hedges |  |
Derivatives, Fair Value [Line Items] |  |
Carrying value of hedged items | 32,829,000 | 35,523,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | (1,468,000) | $ (1,471,000)
Mortgage backed securities fair value hedges |  |
Derivatives, Fair Value [Line Items] |  |
Carrying value of hedged items | 940,110,000 |
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | 15,452,000 |
Amortized cost, designated in portfolio hedging relationship | 610,000,000 |
Loans receivable |  |
Derivatives, Fair Value [Line Items] |  |
Carrying value of hedged items | $ 5,426,086,000 |
Hedged Liability, Statement of Financial Position [Extensible Enumeration] | Loans receivable, net of allowance for loan losses of $199,720 and $203,753 |
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | $ 6,794,000 |
Available-for-sale Securities LOL |  |
Derivatives, Fair Value [Line Items] |  |
Carrying value of hedged items | $ 940,110,000 |
Hedged Liability, Statement of Financial Position [Extensible Enumeration] | Available-for-sale securities, at fair value |
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items | $ 15,452,000 |

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