Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net Financial Instruments	$ 381,991	$ 230,686
Total debt and equity securities	96,012	108,071
Total assets	478,003	338,757
Net Financial Instruments	4,129	5,269
Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	26,367	35,175
Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	32,367	34,298
Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	33,433	35,655
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	3,845	2,943
Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments	0	0
Total debt and equity securities	58,734	69,473
Total assets	58,734	69,473
Financial instruments	0	0
Quoted Prices in Active Markets (Level 1) | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	26,367	35,175
Quoted Prices in Active Markets (Level 1) | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	32,367	34,298
Quoted Prices in Active Markets (Level 1) | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	0	0
Quoted Prices in Active Markets (Level 1) | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	0	0
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments	381,991	230,686
Total debt and equity securities	37,278	38,598
Total assets	419,269	269,284
Financial instruments	4,129	5,269
Significant Other Observable Inputs (Level 2) | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	0	0
Significant Other Observable Inputs (Level 2) | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	0	0
Significant Other Observable Inputs (Level 2) | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	33,433	35,655
Significant Other Observable Inputs (Level 2) | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	3,845	2,943
Significant Other Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments	0	0
Total debt and equity securities	0	0
Total assets	0	0
Financial instruments	0	0
Significant Other Unobservable Inputs (Level 3) | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	0	0
Significant Other Unobservable Inputs (Level 3) | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	0	0
Significant Other Unobservable Inputs (Level 3) | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	0	0
Significant Other Unobservable Inputs (Level 3) | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities	$ 0	$ 0