Annual report pursuant to Section 13 and 15(d)

Convertible Instruments and Accrued Interest - Preferred stock (Detail)

v3.22.2.2
Convertible Instruments and Accrued Interest - Preferred stock (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 12 Months Ended
May 31, 2022
May 31, 2021
Feb. 28, 2022
Nov. 30, 2021
Aug. 31, 2021
Feb. 28, 2021
Nov. 30, 2020
May 31, 2020
Class of Stock [Line Items]                
Accrued dividends $ 3,977 $ 2,647            
Accumulated deficit $ 766,131 553,675 $ 681,622 $ 639,940 $ 599,432 $ 483,183 $ 445,191 $ 375,301
Series B Convertible Preferred Stock                
Class of Stock [Line Items]                
Preferred stock dividend, value per share $ 0.25              
Preferred stock, stated value per share 5.00              
Preferred stock conversion price, per share $ 0.50              
Undeclared dividend $ 10 $ 18            
Shares of common stock 20 36            
Undeclared dividend, shares 10              
Series C Convertible Preferred Stock                
Class of Stock [Line Items]                
Preferred stock dividend rate, as a percent 10.00%              
Preferred stock dividend, value per share $ 0.50              
Preferred stock, stated value per share 1,000              
Preferred stock conversion price, per share $ 0.50              
Accrued dividends $ 2,014 $ 1,530            
Shares of common stock 4,028 3,060            
Series D Convertible Preferred Stock                
Class of Stock [Line Items]                
Preferred stock dividend rate, as a percent 10.00%              
Preferred stock dividend, value per share $ 0.50              
Preferred stock, stated value per share 1,000              
Preferred stock conversion price, per share $ 0.50              
Accrued dividends $ 1,963 $ 1,117            
Shares of common stock 3,926 2,234