Quarterly report pursuant to Section 13 or 15(d)

Weighted Average Assumptions to Value Investor Warrants (Detail)

v3.7.0.1
Weighted Average Assumptions to Value Investor Warrants (Detail) - $ / shares
 6 Months Ended 9 Months Ended 12 Months Ended
Sep. 15, 2016
Nov. 30, 2016
Feb. 28, 2017
May 31, 2016
May 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Expected dividend yield 0.00% 0.00% 0.00%    
Stock price volatility 106.00% 103.00% 101.00%    
Contractual term to maturity (years) 5 years 4 years 9 months 15 days 4 years 6 months 15 days    
Grant-date fair value $ 0.78 $ 0.67 $ 0.71    
Risk-free interest rate 1.20% 1.81% 1.85%    
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]          
Grant-date fair value         $ 0.52
Risk-free interest rate         1.46%
Investor Warrants | Maximum          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Grant-date fair value         $ 0.76
Risk-free interest rate         1.58%
Detachable Common Stock Warrants          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Expected dividend yield       0.00%  
Contractual term to maturity (years)       1 year  
Risk-free interest rate       0.33%  
Detachable Common Stock Warrants | Minimum          
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          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Stock price volatility       69.30%  
Grant-date fair value       $ 0.18