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Goodwill and Intangible Assets, Net - Additional Information (Detail)
12 Months Ended
Sep. 30, 2020
USD ($)
Segment
Sep. 30, 2019
USD ($)
Sep. 30, 2018
USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]      
Impairment of goodwill $ 0 $ 0 $ 0
Number of operating segment | Segment 1    
Amortization of definite-lived purchased intangible assets $ 80,777,000 $ 94,385,000 $ 105,785,000