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)

v3.20.2
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