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Basic and Diluted Earnings Per Share - Additional Information (Detail) - shares
shares in Millions
3 Months Ended
Jul. 31, 2017
Jul. 31, 2016
Restricted Stock    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities excluded from computation of earnings per share, shares 0.6 0.5