Quarterly report pursuant to Section 13 or 15(d)

Reconciliation of Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail)

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Reconciliation of Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($)
 12 Months Ended
May 31, 2020
May 31, 2019
May 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Beginning Balance $ 2,407,000 $ 1,324,000  
Fair value adjustments     $ (3,855,000)
Ending Balance 2,407,000 1,324,000
Convertible notes [Member]      
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Fair value adjustments (2,005,000) (745,000)  
Warrant [Member]      
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Fair value adjustments 11,547,000 (922,000)  
Exercises $ (11,949,000)    
Investor Warrants Issued with Registered Direct Equity Offering      
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Warrants issued     4,360,000
Placement Agent Warrants Issued with Registered Direct Equity Offering      
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Warrants issued     $ 819,000
Inception date value of redemption provision - warrants      
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Warrants issued   $ 2,750,000