Nature of Business and Summary of Significant Accounting Policies - Estimated Useful Life of Definite-Lived Intangible Assets (Detail)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	6 years	6 years
Completed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	5 years	5 years
Completed technology | Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	4 years
Completed technology | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	10 years
Customer contracts and relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	8 years	8 years
Customer contracts and relationships | Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	5 years
Customer contracts and relationships | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	15 years
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life	0 years	3 years
Trade names | Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated useful life