Quarterly report pursuant to Section 13 or 15(d)

Summary of Fair Value Warrant Derivative Liability and Related Common Shares (Detail)

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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