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Loans Receivable - Narrative (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($) portfolioSegment	Sep. 30, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of portfolio segments for loans held for investment | portfolioSegment	2
Accrued interest receivable for loans	$ 92,362	$ 77,349
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	$ 16,957,014	$ 8,941,201
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	$ 98,271	$ 134,860

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- Definition

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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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Amount, after allowance for credit loss, of accrued interest on financing receivable.

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Amount of transactions with related party during the financial reporting period.

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