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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]        
Amortization of intangible assets $ 600 $ 100 $ 1,119 $ 287
Minimum        
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]        
Estimated useful lives of intangible assets (in years)     2 years  
Maximum        
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]        
Estimated useful lives of intangible assets (in years)     6 years