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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 3 Months Ended
Aug. 31, 2017
May 31, 2017
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense, period of remediation, years 5 years  
Estimated liability costs of remediation $ 916,000 $ 916,000
Estimated liability, measurement period, years 15 years  
Estimated liability costs of remediation, current $ 54,000 $ 54,000
Minimum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense 38,000  
Maximum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense $ 57,000