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Marketable Securities - Company's Assets Measured at Fair Value (Detail) - USD ($)
Jun. 30, 2019
Sep. 30, 2018
Investment Holdings [Line Items]    
Total $ 104,767,000 $ 104,058,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 10,476,000 11,768,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,980,000 3,811,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 4,447,000 4,148,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 40,075,000 29,884,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 45,147,000 53,883,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 642,000 564,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 64,692,000 74,174,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 10,476,000 11,768,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,980,000 3,811,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 4,447,000 4,148,000
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 45,147,000 53,883,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 642,000 564,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 40,075,000 29,884,000
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total $ 40,075,000 $ 29,884,000