Fair Value Measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Netting and Cash Collateral	$ 0	$ 0
Financial instruments net assets	3,526	1,619
Debt and equity securities	92,179	99,385
Total assets	95,705	101,004
Netting and Cash Collateral	0	0
Financial instruments net liability	87,195	56,837
Registered investment companies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	37,241	42,644
Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	21,523	21,507
Bonds(2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	30,096	31,400
Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	3,319	3,834
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	58,764	64,151
Total assets	58,764	64,151
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	37,241	42,644
Fair Value Inputs Level 1 | Bond mutual funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	21,523	21,507
Fair Value Inputs Level 1 | Bonds(2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	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	3,526	1,619
Debt and equity securities	33,415	35,234
Total assets	36,941	36,853
Financial instruments gross liability	87,195	56,837
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(2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	30,096	31,400
Fair Value Inputs Level 2 | Money market funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity Securities	3,319	3,834
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(2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	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