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Marketable Securities - Company's Assets Measured at Fair Value (Detail) - USD ($)
Dec. 31, 2018
Sep. 30, 2018
Investment Holdings [Line Items]    
Total $ 104,445,000 $ 104,058,000
Equities [Member]    
Investment Holdings [Line Items]    
Total 15,603,000 11,768,000
Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,832,000 3,811,000
Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 5,759,000 4,148,000
Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total 39,273,000 29,884,000
Government Securities [Member]    
Investment Holdings [Line Items]    
Total 38,900,000 53,883,000
Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 1,078,000 564,000
Level 1 [Member]    
Investment Holdings [Line Items]    
Total 65,172,000 74,174,000
Level 1 [Member] | Equities [Member]    
Investment Holdings [Line Items]    
Total 15,603,000 11,768,000
Level 1 [Member] | Mutual Funds [Member]    
Investment Holdings [Line Items]    
Total 3,832,000 3,811,000
Level 1 [Member] | Exchange Traded Funds [Member]    
Investment Holdings [Line Items]    
Total 5,759,000 4,148,000
Level 1 [Member] | Government Securities [Member]    
Investment Holdings [Line Items]    
Total 38,900,000 53,883,000
Level 1 [Member] | Cash and Money Funds [Member]    
Investment Holdings [Line Items]    
Total 1,078,000 564,000
Level 2 [Member]    
Investment Holdings [Line Items]    
Total 39,273,000 29,884,000
Level 2 [Member] | Corporate Bonds [Member]    
Investment Holdings [Line Items]    
Total $ 39,273,000 $ 29,884,000