Annual report pursuant to Section 13 and 15(d)

Assumptions used in Estimating Fair Value of Warrant Derivative Liability (Detail)

v3.19.2
Assumptions used in Estimating Fair Value of Warrant Derivative Liability (Detail) - $ / shares
 12 Months Ended
Sep. 15, 2016
Sep. 15, 2016
May 31, 2019
May 31, 2018
Grant Date Fair Value        
Derivative [Line Items]        
Fair value of underlying stock   $ 0.78 $ 0.39 $ 0.49
Risk Free Interest Rate        
Derivative [Line Items]        
Risk free rate 1.20%   1.94% 2.63%
Expected Term (In Years)        
Derivative [Line Items]        
Expected term (in years) 5 years   2 years 3 months 14 days 3 years 3 months 18 days
Stock Price Volatility        
Derivative [Line Items]        
Stock price volatility 106.00% 106.00% 61.00% 64.00%
Probability of Fundamental Transaction        
Derivative [Line Items]        
Probability of Fundamental Transaction 50.00%   50.00% 50.00%
Probability of Holder Requesting Cash Payment        
Derivative [Line Items]        
Probability of holder requesting cash payment 50.00%   50.00% 50.00%