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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 6 Months Ended
Nov. 30, 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