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Commitments and Contingencies - Additional Information (Detail) (USD $)
 9 Months Ended
Feb. 28, 2015
May 31, 2014
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense, period of remediation, years 5 years  
Estimated liability costs of remediation $ 916,000us-gaap_AccrualForEnvironmentalLossContingencies $ 916,000us-gaap_AccrualForEnvironmentalLossContingencies
Estimated liability, measurement period, years 15 years  
Minimum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense 47,000us-gaap_EnvironmentalRemediationExpense
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maximum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense $ 79,000us-gaap_EnvironmentalRemediationExpense
/ us-gaap_RangeAxis
= us-gaap_MaximumMember