Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($)	Jun. 30, 2020	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Netting and Cash Collateral	$ 0	$ 0
Financial instruments net assets	5,864,000	1,811,000
Debt and equity securities	105,717,000	101,883,000
Total assets	111,581,000	103,694,000
Netting and Cash Collateral	0	0
Financial instruments net liability	11,103,000	5,801,000
Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	37,229,000	41,406,000
Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	28,954,000	25,966,000
Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	34,408,000	31,915,000
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	5,126,000	2,596,000
Fair Value Inputs Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments gross assets	0	0
Debt and equity securities	66,183,000	67,372,000
Total assets	66,183,000	67,372,000
Financial instruments gross liability	0	0
Fair Value Inputs Level 1 | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	37,229,000	41,406,000
Fair Value Inputs Level 1 | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	28,954,000	25,966,000
Fair Value Inputs Level 1 | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	0	0
Fair Value Inputs Level 1 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	0	0
Fair Value Inputs Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments gross assets	5,864,000	1,811,000
Debt and equity securities	39,534,000	34,511,000
Total assets	45,398,000	36,322,000
Financial instruments gross liability	11,103,000	5,801,000
Fair Value Inputs Level 2 | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	0	0
Fair Value Inputs Level 2 | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	0	0
Fair Value Inputs Level 2 | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	34,408,000	31,915,000
Fair Value Inputs Level 2 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	5,126,000	2,596,000
Fair Value Inputs Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial instruments gross assets	0	0
Debt and equity securities	0	0
Total assets	0	0
Financial instruments gross liability	0	0
Fair Value Inputs Level 3 | Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	0	0
Fair Value Inputs Level 3 | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	0	0
Fair Value Inputs Level 3 | Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt securities	0	0
Fair Value Inputs Level 3 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	$ 0	$ 0