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Commitments and Contingencies - Additional Information (Detail) (USD $)
12 Months Ended
May 31, 2014
May 31, 2013
May 31, 2012
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 costs of remediation, current 50,000 50,000  
Estimated liability, measurement period, years 15 years    
Royalty Expense 2,278,000 1,837,000 1,371,000
Guaranteed minimum royalty payment for period, 2015 658,000    
Guaranteed minimum royalty payment for period, 2016 700,000    
Guaranteed minimum royalty payment for period, 2017 669,000    
Guaranteed minimum royalty payment for period, 2018 769,000    
Office and Manufacturing facilities operating lease expense 856,000 657,000 495,000
Future minimum rental payments for 2015 470,000    
Future minimum rental payments for 2016 324,000    
Future minimum rental payments for 2017 130,000    
Future minimum rental payments for 2018 74,000    
Future minimum rental payments for 2019 and later 96,000    
Minimum
     
Commitments and Contingencies Disclosure [Line Items]      
Environmental remediation expense 47,000    
Maximum
     
Commitments and Contingencies Disclosure [Line Items]      
Environmental remediation expense $ 79,000