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COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024
Commitment and Contingencies [Line Items] |  |
Weighted average remaining lease term | 9 years 1 month 6 days |
Weighted average discount rate | 3.94% |
Operating lease payments | $ 10,758 | $ 9,627
Operating lease liability, statement of financial position [Extensible Enumeration] | Accrued expenses and other liabilities | Accrued expenses and other liabilities
Right-of-use assets obtained in exchange for lease liabilities | $ 19,280 | $ 12,890
Operating lease right-of-use asset, statement of financial position [Extensible Enumeration] | Other assets | Other assets
Right-of-use asset obtained in merger |  | $ 11,478
Rental expense | $ 12,894 | 11,025
Loans receivable, net | 20,088,618 | 20,916,354
Investment, proportional amortization method, elected, amount | $ 157,249 | $ 112,342
Investment, Proportional Amortization Method, Elected, Statement of Financial Position [Extensible Enumeration] | Other assets | Other assets
Investment program, proportional amortization method, elected, commitment | $ 73,123 | $ 41,702
Federal Home Loan Bank Advances |  |
Commitment and Contingencies [Line Items] |  |
Loans receivable, net | 62,606 | 902,606
Unfunded commitments |  |
Commitment and Contingencies [Line Items] |  |
Loans receivable, net | 2,841,596 | $ 2,928,697
Reserve for unfunded commitments | $ 21,500 |

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