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Marketable Securities and Fair Value Measurements - Company's Assets Measured at Fair Value (Detail) - USD ($)
Jun. 30, 2020
Sep. 30, 2019
Investment Holdings [Line Items]    
Total $ 105,675,000 $ 105,322,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 12,089,000 10,412,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,983,000 3,987,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 7,140,000 5,163,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 38,058,000 38,690,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 33,789,000 45,171,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 10,616,000 1,899,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 67,617,000 66,632,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 12,089,000 10,412,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,983,000 3,987,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 7,140,000 5,163,000
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 33,789,000 45,171,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 10,616,000 1,899,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 38,058,000 38,690,000
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 38,058,000 $ 38,690,000
Level 3 [Member]    
Investment Holdings [Line Items]    
Total $ 0