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Marketable Securities - Company's Assets Measured at Fair Value (Detail) - USD ($)
Mar. 31, 2019
Sep. 30, 2018
Investment Holdings [Line Items]    
Total $ 103,156,000 $ 104,058,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 15,172,000 11,768,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,909,000 3,811,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 4,920,000 4,148,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 36,424,000 29,884,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 39,643,000 53,883,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 3,088,000 564,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 66,732,000 74,174,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 15,172,000 11,768,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,909,000 3,811,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 4,920,000 4,148,000
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 39,643,000 53,883,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 3,088,000 564,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 36,424,000 29,884,000
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total $ 36,424,000 $ 29,884,000