Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 35,669	$ 32,636
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]
Amortization of acquisition-related intangible assets	6,439	7,024	$ 4,023
Acquisition-related costs and expenses
Disclosure - Goodwill and Intangible Assets - Additional Information (Detail) [Line Items]
Amortization of acquisition-related intangible assets	$ 6,400	$ 7,000	$ 4,000
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