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Loans Receivable - Narrative (Details) $ in Thousands | 12 Months Ended
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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 Amount, after allowance for credit loss, of accrued interest on financing receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3A -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-3A + Details
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- Definition Amount of transactions with related party during the financial reporting period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-3 + Details
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