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Additional Information Pertaining to Stock Options (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Jan. 31, 2016
Jan. 31, 2015
Jan. 31, 2016
Jan. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total fair value of stock options vested     $ 96 $ 334
Total intrinsic value of stock options exercised $ 73 $ 145 $ 1,631 $ 1,516