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Allowance for Loan Losses - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Sep. 30, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Provision for credit losses | $ 16,000 | $ 3,500 | $ 16,000 | $ 6,000 |
Charge-offs, net of recoveries | 146 | $ 5,877 | 33 | $ 5,388 |
Gross loans | $ 20,996,836 |  | $ 20,996,836 |  | $ 17,653,757
Percent past due | 0.36% |  | 0.36% |  | 0.36%
Financial Asset Originated |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Non-accrual loans | $ 60,806 |  | $ 60,806 |  | $ 50,422
Non-Performing Loans |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Gross loans | $ 68,361 |  | $ 68,361 |  | $ 57,924
Ratio of non-performing assets to total assets | 0.23% |  | 0.23% |  | 0.26%

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