Employee Stock Purchase Plan (Tables)

12 Months Ended

Sep. 30, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Weighted Average Assumptions of Employee Stock Purchase Plan

The following are the weighted-average assumptions used for the fiscal years ended September 30,

	2015		2016		2017
Dividend yield		0.0%		0.0%		0.0%
Risk-free interest rate		0.1%		0.2%		0.7%
Volatility		36.1%		50.9%		40.9%
Expected life	Six months		Six months		Six months