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Earnings per Share - Additional Information (Detail) - shares
shares in Thousands
12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Earnings Per Share [Abstract]      
Options to purchase shares of common stock excluded in the computation of diluted earnings per share because their inclusion would be antidilutive (in shares) 8 9 138