Quarterly report pursuant to Section 13 or 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

v3.19.1
Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
 6 Months Ended 9 Months Ended 12 Months Ended
Sep. 15, 2016
Nov. 30, 2018
Feb. 28, 2019
May 31, 2018
Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term 5 years   2 years 6 months 14 days 3 years 3 months 18 days
Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate 1.20%   2.51% 2.63%
Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value $ 0.78   $ 0.50 $ 0.49
Detachable Common Stock Warrants | Short-Term Convertible Notes | Expected Dividend Yield        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected dividend yield   0.00%    
Detachable Common Stock Warrants | Short-Term Convertible Notes | Stock Price Volatility        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Stock price volatility   69.80%    
Detachable Common Stock Warrants | Short-Term Convertible Notes | Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term   5 years    
Detachable Common Stock Warrants | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Expected Dividend Yield        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected dividend yield     0.00%  
Detachable Common Stock Warrants | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Expected Term (In Years)        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Expected term     5 years  
Detachable Common Stock Warrants | Minimum | 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 | 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 | Minimum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Stock Price Volatility        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Stock price volatility     55.80%  
Detachable Common Stock Warrants | Minimum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate     2.48%  
Detachable Common Stock Warrants | Minimum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value     $ 0.30  
Detachable Common Stock Warrants | Maximum | 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 | Short-Term Convertible Notes | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value   $ 0.39    
Detachable Common Stock Warrants | Maximum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Stock Price Volatility        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Stock price volatility     55.88%  
Detachable Common Stock Warrants | Maximum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Risk Free Interest Rate        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Risk-free interest rate     2.56%  
Detachable Common Stock Warrants | Maximum | Two Thousand And Nineteen Short Term Convertible Notes [Member] | Grant Date Fair Value        
Fair Value Measurement Inputs and Valuation Techniques [Line Items]        
Grant-date fair value     $ 0.38