Nature of Business and Summary of Significant Accounting Policies - Estimated Useful Life of Property and Equipment (Detail)	12 Months Ended
	Sep. 30, 2017
Data processing equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Office furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Office furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	Shorter of estimated useful life or lease term