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Stock Option Activity (Detail) (USD $)
6 Months Ended
Nov. 30, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Shares Outstanding, Beginning Balance 1,543,000
Shares, Granted 306,000
Shares, Exercised (235,000)
Shares, Forfeited (16,000)
Shares outstanding, Ending Balance 1,598,000
Weighted-Average Exercise Price, Beginning Balance $ 22.34
Weighted-Average Exercise Price, Granted $ 43.00
Weighted-Average Exercise Price, Exercised $ 14.43
Weighted-Average Exercise Price, Forfeited $ 27.69
Weighted-Average Exercise Price, Ending Balance $ 27.51