XML 18 R31.htm IDEA: XBRL DOCUMENT v3.3.0.814
Commitments and Contingencies - Additional Information (Detail) - USD ($)
 3 Months Ended
Aug. 31, 2015
May. 31, 2015
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  
Minimum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense $ 47,000  
Maximum    
Commitments and Contingencies Disclosure [Line Items]    
Environmental remediation expense $ 56,000