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LOANS RECEIVABLE - Narrative (Details) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 USD ($) loan portfolioSegment | Sep. 30, 2024 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Number of portfolio segments for loans held for investment | portfolioSegment | 2 |
Accrued interest receivable for loans | $ 85,444 | $ 92,362
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration] | Interest receivable | Interest receivable
Loans pledged to secure borrowings from the Federal Home Loan Bank | $ 13,732,150 | $ 16,957,014
Loans modified in period, amount | 143,305 | 104,492
30 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 22 | 0
60 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 446 | 992
Commercial loans |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 134,585 | 103,610
Commercial loans | 30 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 22 | 0
Commercial loans | 60 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 0 | 992
Commercial loans | Commercial & industrial |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 57,431 | 61,074
Commercial loans | Commercial & industrial | 30 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 22 | 0
Commercial loans | Commercial & industrial | 60 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 0 | 992
Consumer loans |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 8,720 | 882
Consumer loans | 30 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 0 | 0
Consumer loans | 60 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 446 | 0
Consumer loans | Single-family residential |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | 8,720 | 882
Consumer loans | Single-family residential | 30 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified in period, amount | $ 0 | 0
Consumer loans | Single-family residential | 60 Days Delinquent |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans modified, number of loans | loan | 1 |
Loans modified in period, amount | $ 446 | 0
Financing Receivable from Related Party Including Unfunded Loan Commitment |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Loans granted to officers, directors, and related interests | $ 89,608 | $ 98,271

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