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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, 2015
Sep. 30, 2014
Sep. 30, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Risk-free interest rate 0.90% 0.70% 0.60%
Volatility 47.40% 55.70% 80.10%
Expected life 3 years 1 month 6 days 3 years 2 months 12 days 4 years 3 months 18 days