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Employee Benefit Plans - Narrative (Details) |  | 12 Months Ended
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Mar. 09, 2023 $ / shares shares | Sep. 30, 2023 USD ($) installment $ / shares shares | Sep. 30, 2022 USD ($) | Sep. 30, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Employee contribution, percentage of annual salary |  | 100.00% |  |
Employee contribution, maximum allowable contribution | $ |  | $ 66,000 |  |
Service period for participation eligibility |  | 30 days |  |
Service period for eligibility of profit sharing or matching contributions |  | 1 year |  |
Employer matching contribution percent |  | 100.00% |  |
Percent of employees' gross pay |  | 4.00% |  |
Profit sharing contribution, vesting schedule (in years) |  | 6 years |  |
Company contributions to plan | $ |  | $ 8,648,000 | $ 10,559,000 | $ 9,905,000
Employee Stock |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Purchase price of common stock, percent |  | 95.00% |  |
Shares available for issuance (in shares) |  | 500,000 |  |
Shares purchased (in shares) |  | 7,027 |  |
Shares purchased, amount | $ |  | $ 177,021 |  |
Remaining shares available (in shares) |  | 492,973 |  |
SERP |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Number of annual installments | installment |  | 10 |  |
Amount authorized | $ |  | $ 11,700,000 |  |
Units credited in period (in shares) | 368,966 |  |  |
Share price (in dollars per share) | $ / shares | $ 31.71 |  |  |
Units credited in period, dividends (in shares) |  | 7,292 |  |
Units outstanding (in shares) |  | 376,258 |  |
Weighted average grant date fair value (in dollars per share) | $ / shares |  | $ 31.59 |  |
Employee benefits related expenses | $ |  | $ 625,000 |  |

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