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Intangible Assets - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Intangible Assets Net Excluding Goodwill [Abstract]      
Amortization expense recognized $ 0.4 $ 0.4 $ 0.4
Amortization expense for 2019 1.8    
Amortization expense for 2020 1.5    
Amortization expense for 2021 1.2    
Amortization expense for 2022 1.0    
Amortization expense for 2023 $ 0.9