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Marketable Securities - Company's Assets Measured at Fair Value (Detail) - USD ($)
Dec. 31, 2019
Sep. 30, 2019
Investment Holdings [Line Items]    
Total $ 107,232,000 $ 105,322,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 14,070,000 10,412,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 4,052,000 3,987,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 5,298,000 5,163,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 42,474,000 38,690,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 40,005,000 45,171,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 1,333,000 1,899,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 64,758,000 66,632,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 14,070,000 10,412,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 4,052,000 3,987,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 5,298,000 5,163,000
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 40,005,000 45,171,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 1,333,000 1,899,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 42,474,000 38,690,000
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total $ 42,474,000 $ 38,690,000