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Stock Option and Incentive Plan - Summary of Option Activity (Parenthetical) (Detail)
12 Months Ended
Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Weighted average remaining contractual life of outstanding options 7 years 4 months 24 days
Weighted average remaining contractual life of exercisable options 5 years 7 months 28 days