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Stock Option Activity (Parenthetical) (Detail) - shares
shares in Thousands
May. 31, 2015
May. 31, 2014
May. 31, 2013
May. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Shares Outstanding, Exercisable Beginning Balance 639 577 749 863