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The Incentive Stock Plans - Weighted Average Assumptions of Incentive Stock Plans (Detail) - Incentive Stock Plans [Member]
12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Risk-free interest rate 1.00% 0.90% 0.70%
Volatility 48.20% 47.40% 55.70%
Expected life 5 years 3 years 1 month 6 days 3 years 2 months 12 days