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Goodwill and Intangible Assets - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]      
Goodwill $ 63,096 $ 35,669  
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]      
Amortization of intangible assets 7,505 6,439 $ 7,024
Acquisition-related costs and expenses      
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]      
Amortization of intangible assets $ 7,500 $ 6,400 $ 7,000
Minimum      
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]      
Estimated useful lives of intangible assets 2 years    
Maximum      
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]      
Estimated useful lives of intangible assets 7 years