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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 6 Months Ended
Oct. 31, 2012
Oct. 31, 2011
Oct. 31, 2012
Oct. 31, 2011
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Weighted-average fair value of stock options granted       $ 9.61
Total fair value of stock options vested $ 78 $ 78 $ 907 $ 894
Total intrinsic value of stock options exercised $ 751 $ 11 $ 911 $ 859