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Marketable Securities and Fair Value Measurements - Company's Assets Measured at Fair Value (Detail) - USD ($)
Mar. 31, 2022
Sep. 30, 2021
Investment Holdings [Line Items]    
Total $ 94,501,000 $ 94,976,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 19,998,000 14,734,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 10,130,000 10,357,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 9,849,000 9,458,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 24,022,000 24,853,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 27,960,000 30,999,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 2,542,000 4,575,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 70,479,000 70,123,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 19,998,000 14,734,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 10,130,000 10,357,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 9,849,000 9,458,000
Level 1 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 27,960,000 30,999,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 2,542,000 4,575,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 24,022,000 24,853,000
Level 2 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 2 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 2 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 24,022,000 24,853,000
Level 2 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 2 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 0 0
Level 3 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total $ 0 $ 0