LOANS RECEIVABLE - Narrative (Details) $ in Thousands	12 Months Ended
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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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