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Commitments and Contingencies - Additional Information (Detail) (USD $)
 9 Months Ended
Feb. 28, 2013
Y
May 31, 2012
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense, period of remediation, years 5  
Estimated liability costs of remediation $ 916,000 $ 916,000
Estimated liability, measurement period, years 15  
Minimum
    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense 50,000  
Maximum
    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense $ 105,000