Assumptions used in Estimating Fair Value of Warrant Derivative Liability (Detail) - $ / shares		12 Months Ended
	Sep. 15, 2016	May 31, 2018	May 31, 2017
Grant Date Fair Value
Derivative [Line Items]
Fair value of underlying stock	$ 0.78	$ 0.49	$ 0.60
Risk Free Interest Rate
Derivative [Line Items]
Risk free rate	1.20%	2.63%	1.71%
Expected Term (In Years)
Derivative [Line Items]
Expected term (in years)	5 years	3 years 3 months 18 days	4 years 3 months 14 days
Stock Price Volatility
Derivative [Line Items]
Stock price volatility	106.00%	64.00%	94.00%
Expected Dividend Yield
Derivative [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
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%