Quarterly report pursuant to Section 13 or 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

v3.8.0.1
Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
9 Months Ended 12 Months Ended
Sep. 15, 2016
Feb. 28, 2018
May 31, 2017
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Expected dividend yield 0.00% 0.00% 0.00%
Stock price volatility 106.00% 75.00% 94.00%
Expected term 5 years 3 years 6 months 14 days 4 years 3 months 15 days
Risk-free interest rate 1.20% 2.58% 1.71%
Grant-date fair value $ 0.78 $ 0.79 $ 0.60
Detachable Common Stock Warrants | Short-Term Convertible Notes      
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Expected dividend yield   0.00%  
Expected term   5 years  
Detachable Common Stock Warrants | Minimum | Short-Term Convertible Notes      
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Stock price volatility   69.50%  
Risk-free interest rate   1.75%  
Grant-date fair value   $ 0.28  
Detachable Common Stock Warrants | Maximum | Short-Term Convertible Notes      
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]      
Stock price volatility   69.80%  
Risk-free interest rate   1.83%  
Grant-date fair value   $ 0.39