Annual report pursuant to Section 13 and 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

v3.10.0.1
Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
 12 Months Ended
Sep. 15, 2016
May 31, 2018
May 31, 2017
May 31, 2015
Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term 5 years 3 years 3 months 18 days 4 years 3 months 14 days  
Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate 1.20% 2.63% 1.71%  
Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value $ 0.78 $ 0.49 $ 0.60  
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes | Expected Dividend Yield        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected dividend yield   0.00% 0.00%  
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes | Stock Price Volatility        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Stock price volatility   69.80% 69.00%  
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes | Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term   5 years 5 years  
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate     1.75%  
Detachable Common Stock Warrants | 2017 Short Term Convertible Notes | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value     $ 0.24  
Detachable Common Stock Warrants | Minimum | 2017 Short Term Convertible Notes | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate   1.77%    
Detachable Common Stock Warrants | Minimum | 2017 Short Term Convertible Notes | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value   $ 0.30    
Detachable Common Stock Warrants | Maximum | 2017 Short Term Convertible Notes | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate   1.93%    
Detachable Common Stock Warrants | Maximum | 2017 Short Term Convertible Notes | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value   $ 0.39    
Investor Warrants | Expected Dividend Yield        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected dividend yield       0.00%
Investor Warrants | Stock Price Volatility        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Stock price volatility       88.79%
Investor Warrants | Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term       5 years
Investor Warrants | Minimum | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate       1.46%
Investor Warrants | Minimum | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value       $ 0.52
Investor Warrants | Maximum | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate       1.58%
Investor Warrants | Maximum | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value       $ 0.76