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 ($) $ in Thousands	12 Months Ended	33 Months Ended
	May 31, 2020	May 31, 2019	Sep. 15, 2016
Derivative [Line Items]
Shares Indexed		7,733,000	7,733,000
Fair value of warrants exercised	7,733,000
Change in fair value of derivative liability	$ 11,547	$ (4,777)
Fair value of warrants exercised	$ (11,949)
Derivative liability		$ 402	$ 5,179