Annual report pursuant to Section 13 and 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

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Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
12 Months Ended
May. 31, 2015
May. 31, 2014
Debt and Financial Instruments [Line Items]    
Expected dividend yield 0.00% 0.00%
Stock price volatility 80.68%  
Expected term 6 months  
Risk-free interest rate 0.12%  
Grant-date fair value $ 0.15  
Investor warrants    
Debt and Financial Instruments [Line Items]    
Expected dividend yield 0.00%  
Stock price volatility 88.79%  
Expected term 5 years  
Minimum    
Debt and Financial Instruments [Line Items]    
Stock price volatility   78.00%
Expected term   3 years
Risk-free interest rate   0.64%
Grant-date fair value   $ 0.66
Minimum | Investor warrants    
Debt and Financial Instruments [Line Items]    
Risk-free interest rate 1.46%  
Grant-date fair value $ 0.52  
Maximum    
Debt and Financial Instruments [Line Items]    
Stock price volatility   93.00%
Expected term   5 years
Risk-free interest rate   1.42%
Grant-date fair value   $ 0.72
Maximum | Investor warrants    
Debt and Financial Instruments [Line Items]    
Risk-free interest rate 1.58%  
Grant-date fair value $ 0.76