Employee Benefit Plans - Narrative (Details)		12 Months Ended
	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