Annual report pursuant to Section 13 and 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

v3.7.0.1
Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
 12 Months Ended
Sep. 15, 2016
May 31, 2017
May 31, 2016
May 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected dividend yield 0.00% 0.00%    
Stock price volatility 106.00% 94.00%    
Contractual term to maturity (years) 5 years 4 years 3 months 15 days    
Risk-free interest rate 1.20% 1.71%    
Grant-date fair value $ 0.78 $ 0.60    
Investor Warrants        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected dividend yield       0.00%
Stock price volatility       88.79%
Contractual term to maturity (years)       5 years
Investor Warrants | Minimum        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Risk-free interest rate       1.46%
Grant-date fair value       $ 0.52
Investor Warrants | Maximum        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Risk-free interest rate       1.58%
Grant-date fair value       $ 0.76
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected dividend yield   0.00%    
Stock price volatility   69.00%    
Contractual term to maturity (years)   5 years    
Risk-free interest rate   1.75%    
Grant-date fair value   $ 0.24    
Detachable Common Stock Warrants | 2013 Convertible Notes        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Expected dividend yield   0.00% 0.00%  
Stock price volatility   4.00%    
Contractual term to maturity (years)   1 month 1 year  
Risk-free interest rate   77.00% 0.33%  
Grant-date fair value   $ 0.11    
Detachable Common Stock Warrants | Minimum | 2013 Convertible Notes        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Stock price volatility     64.56%  
Grant-date fair value     $ 0.15  
Detachable Common Stock Warrants | Maximum | 2013 Convertible Notes        
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]        
Stock price volatility     69.30%  
Grant-date fair value     $ 0.18