Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.20.2
Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 3 Months Ended
Aug. 31, 2020
Aug. 31, 2019
May 31, 2020
Jan. 28, 2020
Apr. 30, 2010
Summary Of Significant Accounting Policies [Line Items]          
Net loss $ (30,832,000) $ (16,164,000)      
Accumulated (deficit) (386,206,000)   $ (354,711,000)    
Balance in excess of federally insured limits 18,000,000.0   14,000,000.0    
Impairment charges 0 0      
Pre-launch inventory qualified for capitalization $ 0   $ 0    
Estimated future unvested forfeitures 0.00%        
Common stock, shares authorized 800,000,000   800,000,000    
Common stock, shares outstanding 569,883,000   518,976,000    
Preferred Stock Shares authorized to be issued 5,000,000   5,000,000    
Treasury stock, par value $ 0.001        
Treasury stock, shares 442,578        
Debt discount $ 1,700,000        
Amortization of discount on convertible notes 1,339,000 1,030,000      
Amortization of debt issuance costs $ 4,000 $ 284,000      
Federal statutory income tax rate, percent 21.00% 21.00%      
Deferred income tax benefit $ 0 $ 0      
Common stock options and warrants to purchase 87,000,000 155,000,000      
Equity Securities          
Summary Of Significant Accounting Policies [Line Items]          
Deferred offering costs $ 400,000   $ 2,300,000    
Short-Term Convertible Notes          
Summary Of Significant Accounting Policies [Line Items]          
Direct costs associated with the convertible notes 100,000        
Amortization of debt issuance costs 4,000 $ 284,000      
Short-Term Convertible Notes | Detachable Common Stock Warrants          
Summary Of Significant Accounting Policies [Line Items]          
Debt discount 3,400,000        
Amortization of discount on convertible notes $ 1,300,000 $ 1,000,000.0      
Series B Convertible Preferred Stock          
Summary Of Significant Accounting Policies [Line Items]          
Common stock, shares authorized         100,000,000
Preferred Stock Shares authorized to be issued 400,000   400,000    
Preferred stock, shares outstanding 87,000   92,000    
Series B Convertible Preferred Stock | Equity Securities          
Summary Of Significant Accounting Policies [Line Items]          
Preferred stock, shares outstanding 87,100        
Series C Convertible Preferred Stock          
Summary Of Significant Accounting Policies [Line Items]          
Preferred Stock Shares authorized to be issued 11,737        
Preferred stock, shares outstanding 8,203        
Common Stock          
Summary Of Significant Accounting Policies [Line Items]          
Common stock, shares authorized 800,000,000        
Common stock, shares outstanding 569,882,808        
Common shares issued upon conversion of debt securities 9,800,000 11,600,000      
Common shares issued upon conversion of preferred stock 30,300,000 11,700,000      
Series D Convertible Preferred Stock          
Summary Of Significant Accounting Policies [Line Items]          
Preferred Stock Shares authorized to be issued 12,000   12,000 11,737  
Preferred stock, shares outstanding 9,000   9,000    
Series D Convertible Preferred Stock | Equity Securities          
Summary Of Significant Accounting Policies [Line Items]          
Preferred stock, shares outstanding 8,452        
Maximum          
Summary Of Significant Accounting Policies [Line Items]          
Preferred Stock Shares authorized to be issued 5,000,000