Annual report pursuant to Section 13 and 15(d)

Equity Awards - Private Placement of Shares of Common Stock and Warrants (Details)

v3.22.2.2
Equity Awards - Private Placement of Shares of Common Stock and Warrants (Details)
1 Months Ended 12 Months Ended
Mar. 25, 2022
shares
Feb. 04, 2022
shares
May 31, 2021
USD ($)
$ / shares
shares
Feb. 28, 2022
USD ($)
$ / shares
shares
May 31, 2022
USD ($)
item
$ / shares
shares
May 31, 2021
USD ($)
$ / shares
shares
May 31, 2020
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Warrant exercises, shares         1,400,000 26,700,000  
Warrant exercises, value | $         $ 1,036,000 $ 18,649,000 $ 20,500,000
Exercise of warrants for cash | $         $ 1,000,000.0    
Cashless exercise of warrants, shares         200,000    
Cashless exercise of warrants, warrants         300,000    
Shares issued during the period new issues shares         7,900,000    
Finance charges related to warrant issuance for surety bond backstop agreement | $         $ 6,585,000    
Proceeds from warrant exercises | $         $ 1,036,000 19,428,000 38,422,000
Number Of Warrants In Fixed Combination Issue Of Securities         0.3    
Proceeds from warrant transactions | $         $ 5,390,000 $ 17,060,000  
Warrant covering common stock shares purchased, percentage         12.00%    
Stock issued via offering, tender or placement, value | $             13,409,000
Former Chief Executive Officer [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Compensation policy period         18 months    
Shares issued during the period new issues shares 908,418            
Former General Counsel [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Compensation policy period         12 months    
Severance payment | $         $ 12,500    
Shares issued during the period new issues shares         155,612    
Registered Direct Offering [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock issued via offering, tender or placement, value | $             12,666,000
Private Equity Offering              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares issued during the period new issues shares           8,900,000  
Stock based compensation | $       $ 14,000      
Term of warrants     5 years     5 years  
Proceeds from warrant exercises | $           $ 23,600,000  
Number of common shares in a fixed combination issue of shares     1     1  
Number Of Warrants In Fixed Combination Issue Of Securities     1     1  
Stock issued via offering, tender or placement, value | $         $ 46,511,000 $ 1,000,000  
Private Equity Offering | Consultant              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares       $ 1.04      
Shares issued during the period new issues shares       15,000      
Common stock warrants to purchase shares       25,000      
Private Equity Offering | Placement Agent              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 0.40    
Warrant exercises, shares         11,400,000    
Shares issued during the period new issues shares         38,100,000    
Common stock warrants to purchase shares         1,600,000    
Term of warrants         7 years    
Non-cash inducement interest expense | $         $ 1,700,000    
Cash inducement interest expense | $         $ 200,000    
Accredited Investors [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Warrant exercises, shares           2,300,000  
Shares issued during the period new issues shares     4,100,000   3,500,000 8,800,000  
Common stock warrants to purchase shares     900,000     900,000  
Non-cash inducement interest expense | $         $ 5,200,000    
Stock issued via offering, tender or placement, value | $         5,400,000    
Private Warrant Exchange [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Warrant exercises, value | $         $ 5,390,000 $ 17,556,000  
Warrants exchanged (in shares)         3,500,000 32,600,000  
Shares issued during the period new issues shares     36,200,000     35,800,000  
Common stock warrants to purchase shares         7,900,000    
Non-cash inducement interest expense | $           $ 14,000,000.0  
Proceeds from warrant transactions | $           16,200,000  
Placement agent fees and expenses | $           500,000  
Stock issued via offering, tender or placement, value | $     $ 34,900,000       6,021,000
Private Warrant Exchange [Member] | Placement Agent              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Non-cash inducement interest expense | $         $ 6,700,000 13,900,000  
Private Warrant Exchange, Non-Inducement Shares [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Shares issued during the period new issues shares     400,000        
Non-cash inducement interest expense | $         $ 1,500,000    
Allotment to placement agent              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 0.255    
Increase in number of shares authorized         350,000,000    
Term of warrants         10 years    
Warrant covering common stock shares purchased, percentage         13.00%    
Placement agent fees and expenses | $         $ 50,000    
Allotment to placement agent | Placement Agent              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 1.00    
Shares issued during the period new issues shares         1,400,000    
Term of warrants         10 years    
Warrant covering common stock shares purchased, percentage         12.00%    
Public Warrant Tender Offering [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock issued via offering, tender or placement, value | $           $ 828,000 $ 11,900,000
Second Private Placement [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 0.30    
Exercise price of stock warrant combo, per share | $ / shares         $ 0.255    
Shares issued during the period new issues shares         34,600,000    
Term of warrants         5 years    
Proceeds from warrant exercises | $         $ 8,800,000    
Number of common shares in a fixed combination issue of shares         1    
Number Of Warrants In Fixed Combination Issue Of Securities         1    
Proceeds from warrant transactions | $         $ 7,600,000    
Warrant exercise price percentage of final unit price         120.00%    
Stock Subscription Agreements [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 1.00    
Number of private placements conducted | item         2    
Shares issued during the period new issues shares         11,400,000    
Common stock warrants to purchase shares         5,000,000.0    
Number of common shares in a fixed combination issue of shares         1    
Proceeds from warrant transactions | $         $ 1,400,000    
Placement agent fees and expenses | $         50,000    
Proceeds from Issuance of Common Stock | $         11,400,000    
Stock issued via offering, tender or placement, value | $         10,000,000.0    
Surety Bond Backstop Agreement [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock based compensation | $         $ 6,600,000    
Common stock warrants to purchase shares         15,000,000    
Interest rate   10.00%          
Period of Indemnification, Payment by Indemnitors   90 days          
Indemnification Fee Payment Ratio   1.50%          
Initial Warrant [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Common stock warrants to purchase shares   15,000,000          
Make-Whole Warrant [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Common stock warrants to purchase shares   15,000,000          
Four Good Warrants [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         $ 0.20    
Finance charges related to warrant issuance for surety bond backstop agreement | $         $ 6,600,000    
Term of warrants         5 years    
Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     $ 1.00   $ 1.35 $ 1.00  
Cashless exercise of warrants, exercise price | $ / shares         0.83    
Maximum | Private Equity Offering              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     1.80     1.80  
Maximum | Accredited Investors [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     1.00   1.00 1.00  
Maximum | Private Warrant Exchange [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     0.90     0.90  
Warrants grant date fair value | $ / shares     1.50     1.50  
Maximum | Four Good Warrants [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares         0.30    
Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     0.45   0.45 0.45  
Cashless exercise of warrants, exercise price | $ / shares         0.40    
Minimum | Private Equity Offering              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     0.40     0.40  
Minimum | Accredited Investors [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     0.40   $ 0.45 0.40  
Minimum | Private Warrant Exchange [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Exercise price of warrants, per share | $ / shares     0.21     0.21  
Warrants grant date fair value | $ / shares     $ 0.30     $ 0.30