Nature of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Accounting Policies [Abstract]
Depreciation and amortization, property and equipment	$ 17.7	$ 20.2	$ 20.7
Property, Plant and Equipment [Line Items]
Foreign Currency Transaction Gain (Loss), before Tax	0.2	0.0	(1.0)
Advertising and promotion costs	$ 3.6	$ 3.7	$ 3.8
Minimum
Property, Plant and Equipment [Line Items]
Stock option awards vesting period	3 years
Maximum
Property, Plant and Equipment [Line Items]
Stock option awards vesting period	4 years
Internal-use Software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	2 years
Internal-use Software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years