Stock-based Compensation - Assumptions Used in Stock Option Plans (Detail)	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rates	1.20%	1.60%	1.40%	1.20%
Expected life (years)	4 years 4 months 24 days	4 years 9 months 18 days	4 years 6 months	4 years 7 months 6 days
Expected volatility	38.50%	43.90%	43.20%	44.50%
Dividend yield	0.00%	0.00%	0.00%	0.00%