Summary of Fair Value Warrant Derivative Liability and Related Common Shares (Detail) - Registered Direct Equity Offering - Investor Warrants Issued with Registered Direct Equity Offering - USD ($)	May 31, 2019	May 31, 2018	Sep. 15, 2016
Derivative [Line Items]
Shares indexed	7,733,334	7,733,334	7,333,334
Derivative liability	$ 402,132	$ 1,323,732	$ 5,179,200