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Additional Information Pertaining to Stock Options and SARs (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended
Jul. 31, 2012
Jul. 31, 2011
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]    
Weighted-average fair value per share of stock options granted   $ 9.61
Total fair value of stock options vested $ 829 $ 816
Total intrinsic value of stock options exercised $ 160 $ 848