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Investments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]        
Other-than-temporary impairment charges recognized $ 0 $ 0 $ 0 $ 0
Gain (loss) on sale of debt investments (26,000)   (49,000) $ 0
Other current liabilities        
Acquired Indefinite-lived Intangible Assets [Line Items]        
Acquisition-related contingent consideration, current 1,900,000   1,900,000  
Other non-current liabilities        
Acquired Indefinite-lived Intangible Assets [Line Items]        
Acquisition-related contingent consideration, noncurrent $ 500,000   $ 500,000