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Employee Benefit Plans - Narrative (Details)
 12 Months Ended
Sep. 30, 2024
USD ($)
installment
$ / shares
shares
Sep. 30, 2023
USD ($)
Sep. 30, 2022
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Employee contribution, percentage of annual salary 100.00%    
Employee contribution, maximum allowable contribution | $ $ 69,000    
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 | $ $ 8,185,000 $ 8,648,000 $ 10,559,000
Employee Stock      
Defined Benefit Plan Disclosure [Line Items]      
Purchase price of common stock, percent 95.00%    
Shares available for issuance (in shares) | shares 500,000    
Shares purchased (in shares) | shares 35,782    
Shares purchased, amount | $ $ 956,550    
Remaining shares available (in shares) | shares 457,191    
SERP      
Defined Benefit Plan Disclosure [Line Items]      
Number of annual installments | installment 10    
Amount authorized | $ $ 11,700,000    
Units credited in period (in shares) | shares 12,710    
Units outstanding (in shares) | shares 388,968    
Weighted average grant date fair value (in dollars per share) | $ / shares $ 31.56    
Employee benefits related expenses | $ $ 1,013,000