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Investments - Summary of Investments (Detail) (USD $)
In Thousands, unless otherwise specified
Aug. 31, 2013
May 31, 2013
Schedule of Held-to-maturity Securities [Line Items]    
Gross Amortized Costs $ 7,000 $ 4,000
U. S. Treasury Bills [Member]
    
Schedule of Held-to-maturity Securities [Line Items]    
Gross Amortized Costs 7,000 4,000
Gross Unrealized Gains      
Fair Value $ 7,000 $ 4,000