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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 3 Months Ended
Aug. 31, 2020
May 31, 2020
Aug. 31, 2019
May 31, 2019
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   $ 100,000    
Minimum        
Commitments and Contingencies Disclosure [Line Items]        
Environmental remediation expense $ 38,000      
Maximum        
Commitments and Contingencies Disclosure [Line Items]        
Environmental remediation expense $ 131,000