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ALLOWANCE FOR LOAN LOSSES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Provision for credit losses | $ 7,750 | $ 17,500 | $ 41,500
Allowance for credit loss, charge-off (recovery) | 11,783 | 1,356 |
Gross loans | 20,288,338 | 21,120,107 |
Allowance for loan losses | 199,720 | 203,753 | $ 177,207
Loans Subject to Quantitative Evaluation |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Allowance for loan losses | 131,652 |  |
Loans Subject to Management Qualitative Evaluation |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Allowance for loan losses | 68,068 |  |
Non-Performing Loans |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Gross loans | $ 143,022 | $ 77,418 |
Ratio of non-performing assets to total assets | 0.54% | 0.28% |
Financial Asset Originated |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |
Non-accrual loans | $ 128,628 | $ 69,541 |

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- Definition Amount, excluding accrued interest, of decrease (increase) in allowance for credit loss on financing receivable from writeoff (recovery). Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-13 + Details
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