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Commitments and Contingencies - Additional Information (Detail) - USD ($)
 12 Months Ended
May 31, 2021
May 31, 2020
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 $ 300,000    
Royalty Expense 2,129,000 $ 2,524,000 $ 2,795,000
Future minimum royalty payment for period, 2022 115,000    
Future minimum royalty payment for period, 2023 110,000    
Future minimum royalty payment for period, 2024 110,000    
Future minimum royalty payment for period, 2025 110,000    
Future minimum royalty payment for period, 2026 85,000    
Estimated liability costs of remediation, non current 616,000    
Environmental loss contingencies, charges to expense for potential fines or penalties 600,000    
Minimum      
Commitments and Contingencies Disclosure [Line Items]      
Environmental remediation expense 38,000    
Maximum      
Commitments and Contingencies Disclosure [Line Items]      
Environmental remediation expense $ 131,000