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Earnings Per Share - Additional Information (Detail) - shares
3 Months Ended 9 Months Ended
Jan. 31, 2017
Jan. 31, 2016
Jan. 31, 2017
Jan. 31, 2016
Earnings Per Share [Abstract]        
Anti-dilutive options exclude from computation of earning per share 39,200 111,400 39,200 111,400