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Income Taxes - Additional Information (Detail) (USD $)
 12 Months Ended
May 31, 2013
May 31, 2012
May 31, 2011
Income Taxes [Line Items]      
Uncertain tax positions, reserves   $ 550,000  
Uncertain tax position, tax rate   33.70%  
Effective tax rate 34.30% 35.50% 35.20%