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Earnings Per Share - Additional Information (Detail) (Stock Options [Member])
3 Months Ended 6 Months Ended
Oct. 31, 2013
Oct. 31, 2012
Oct. 31, 2013
Oct. 31, 2012
Stock Options [Member]
       
Earnings Per Share [Line Items]        
Antidilutive options exclude from computation of earning per share 48,050 158,400 48,050 158,400