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Additional Information Pertaining to Stock Options (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Jul. 31, 2014
Jul. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total fair value of stock options vested $ 324 $ 802
Total intrinsic value of stock options exercised $ 1,039 $ 1,664