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Stock-Based Compensation - Assumptions Used to Value Stock Options (Detail) - $ / shares
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate, minimum 1.34% 1.05% 1.46%
Risk-free interest rate, maximum 2.31% 1.89% 1.89%
Volatility 79.00% 89.00% 75.00%
Expected life (in years) 5 years 10 months 6 days 6 years 3 months  
Weighted average grant date fair value per share of options granted $ 1.33 $ 4.58 $ 4.24
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected life (in years)     6 years
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected life (in years)     6 years 3 months