| Consolidated Statement of Changes in Stockholders Deficit - USD ($)shares in Thousands, $ in Thousands
 | Preferred Stock  Series B Convertible Preferred Stock | Preferred Stock  Series C Convertible Preferred Stock | Preferred Stock | Common Stock  Series B Convertible Preferred Stock | Common Stock  Series C Convertible Preferred Stock | Common Stock  Private Warrant Exchange [Member] | Common Stock  Private Equity Offering | Common Stock | Treasury Stock | Additional Paid-in Capital  Series C Convertible Preferred Stock | Additional Paid-in Capital  Private Warrant Exchange [Member] | [1] | Additional Paid-in Capital  Private Equity Offering | Additional Paid-in Capital | Accumulated Deficit | Series B Convertible Preferred Stock | [1] | Private Warrant Exchange [Member] | Private Equity Offering | Total | 
| Beginning balance at May. 31, 2021 |  |  |  |  |  |  |  |  | $ 626 |  |  |  |  |  | $ 532,031 | [1] | $ (553,675) | [1] |  |  |  |  |  | $ (21,018) | [1] | 
| Beginning balance (shares) at May. 31, 2021 |  |  |  | 96 |  |  |  |  | 626,123 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Issuance of stock for convertible note repayment |  |  |  |  |  |  |  |  | $ 12 |  |  |  |  |  | 13,832 | [1] |  |  |  |  |  |  |  | 13,844 | [1] | 
| Issuance of stock for convertible note repayment (in shares) |  |  |  |  |  |  |  |  | 11,816 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Loss on induced conversion | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 18,530 |  |  |  |  |  |  |  |  | 18,530 |  | 
| Issuance of legal settlement, warrants | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,744 |  |  |  |  |  |  |  |  | 1,744 |  | 
| Stock option exercises | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 189 |  |  |  |  |  |  |  |  | 189 |  | 
| Stock option exercises (in shares) |  |  |  |  |  |  |  |  | 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock issued for compensation and tendered for income tax |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  | (1) | [1] |  |  |  |  |  |  |  |  |  | 
| Stock issued for compensation and tendered for income tax (in shares) |  |  |  |  |  |  |  |  | 1,014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock issued for private offerings |  |  |  |  |  |  |  | $ 3 |  |  |  |  | $ 2,869 | [1] |  |  |  |  |  |  |  | $ 2,872 | [1] |  |  | 
| Stock issued for private offerings (in shares) |  |  |  |  |  |  |  | 2,872 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Warrant exercises |  |  |  |  |  |  | $ 1 |  | $ 1 |  |  | $ 774 |  |  | 502 | [1] |  |  |  | $ 775 | [1] |  |  | 503 | [1] | 
| Warrant exercises (in shares) |  |  |  |  |  |  | 1,327 |  | 668 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Inducement interest expense related to private warrant exchange | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 528 |  |  |  |  |  |  |  |  | 528 |  | 
| Dividends accrued on Series C and D convertible preferred stock | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (420) |  |  |  |  |  |  | (420) |  | 
| Stock-based compensation | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,597 |  |  |  |  |  |  |  |  | 2,597 |  | 
| Net loss | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (45,337) |  |  |  |  |  |  | (45,337) |  | 
| Ending balance at Aug. 31, 2021 |  |  |  |  |  |  |  |  | $ 644 |  |  |  |  |  | 573,595 | [1] | (599,432) | [1] |  |  |  |  |  | (25,193) | [1] | 
| Ending balance (shares) at Aug. 31, 2021 |  |  |  | 96 |  |  |  |  | 644,120 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at May. 31, 2021 |  |  |  |  |  |  |  |  | $ 626 |  |  |  |  |  | 532,031 | [1] | (553,675) | [1] |  |  |  |  |  | (21,018) | [1] | 
| Beginning balance (shares) at May. 31, 2021 |  |  |  | 96 |  |  |  |  | 626,123 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Loss on induced conversion | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,315 |  | 
| Net loss | [1],[2] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (85,414) |  | 
| Ending balance at Nov. 30, 2021 |  |  |  |  |  |  |  |  | $ 686 |  |  |  |  |  | 626,558 | [1] | (639,940) | [1] |  |  |  |  |  | (12,696) | [1] | 
| Ending balance (shares) at Nov. 30, 2021 |  |  |  | 36 |  |  |  |  | 685,861 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at May. 31, 2021 |  |  |  |  |  |  |  |  | $ 626 |  |  |  |  |  | 532,031 | [1] | (553,675) | [1] |  |  |  |  |  | (21,018) | [1] | 
| Beginning balance (shares) at May. 31, 2021 |  |  |  | 96 |  |  |  |  | 626,123 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Ending balance at May. 31, 2022 |  |  |  |  |  |  |  |  | $ 720 |  |  |  |  |  | 671,013 |  | (766,131) |  |  |  |  |  |  | (94,398) |  | 
| Ending balance (shares) at May. 31, 2022 |  |  |  | 35 |  |  |  |  | 720,028 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at Aug. 31, 2021 |  |  |  |  |  |  |  |  | $ 644 |  |  |  |  |  | 573,595 | [1] | (599,432) | [1] |  |  |  |  |  | (25,193) | [1] | 
| Beginning balance (shares) at Aug. 31, 2021 |  |  |  | 96 |  |  |  |  | 644,120 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Issuance of stock for convertible note repayment |  |  |  |  |  |  |  |  | $ 8 |  |  |  |  |  | 8,193 | [1] |  |  |  |  |  |  |  | 8,201 | [1] | 
| Issuance of stock for convertible note repayment (in shares) |  |  |  |  |  |  |  |  | 8,162 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Loss on induced conversion | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,785 |  |  |  |  |  |  |  |  | 6,785 |  | 
| Stock option exercises | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 200 |  |  |  |  |  |  |  |  | 200 |  | 
| Stock option exercises (in shares) |  |  |  |  |  |  |  |  | 210 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock issued for private offerings |  |  |  |  |  |  |  | $ 25 |  |  |  |  | 27,282 | [1] |  |  |  |  |  |  |  | 27,307 | [1] |  |  | 
| Stock issued for private offerings (in shares) |  |  |  |  |  |  |  | 25,178 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Issuance costs related to stock issued for private offerings | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | (1,418) |  |  |  |  |  |  |  |  | (1,418) |  | 
| Conversion of preferred stock to common stock |  |  |  |  | $ 1 |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  |  | 
| Conversion of preferred stock to common stock (in shares) |  | (60) |  |  | 600 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Warrant exercises |  |  |  |  |  |  | $ 7 |  | $ 1 |  |  | $ 4,608 |  |  | 532 | [1] |  |  |  | $ 4,615 | [1] |  |  | 533 | [1] | 
| Warrant exercises (in shares) |  |  |  |  |  |  | 6,593 |  | 963 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Inducement interest expense related to private warrant exchange | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,704 |  |  |  |  |  |  |  |  | 4,704 |  | 
| Dividends accrued on Series C and D convertible preferred stock | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 17 |  | (431) |  |  |  |  |  |  | (414) |  | 
| Dividends accrued on Series C and D convertible preferred stock (in shares) |  |  |  |  |  |  |  |  | 35 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock-based compensation | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,060 |  |  |  |  |  |  |  |  | 2,060 |  | 
| Net loss | [1] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (40,077) |  |  |  |  |  |  | (40,077) | [2] | 
| Ending balance at Nov. 30, 2021 |  |  |  |  |  |  |  |  | $ 686 |  |  |  |  |  | 626,558 | [1] | (639,940) | [1] |  |  |  |  |  | (12,696) | [1] | 
| Ending balance (shares) at Nov. 30, 2021 |  |  |  | 36 |  |  |  |  | 685,861 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at May. 31, 2022 |  |  |  |  |  |  |  |  | $ 720 |  |  |  |  |  | 671,013 |  | (766,131) |  |  |  |  |  |  | (94,398) |  | 
| Beginning balance (shares) at May. 31, 2022 |  |  |  | 35 |  |  |  |  | 720,028 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock issued for compensation |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  | 344 |  |  |  |  |  |  |  |  | $ 345 |  | 
| Stock issued for compensation (in shares) |  |  |  |  |  |  |  |  | 879 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Stock issued for private offerings |  |  |  |  |  |  |  | $ 85 |  |  |  |  | $ 17,459 |  |  |  |  |  |  |  |  | $ 17,544 |  |  |  | 
| Stock issued for private offerings (in shares) |  |  |  |  |  |  |  | 85,378 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,600 |  | 
| Issuance costs related to stock issued for private offerings |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (6,289) |  |  |  |  |  |  |  |  | $ (6,289) |  | 
| Conversion of preferred stock to common stock |  |  |  |  |  | $ 1 |  |  |  |  | $ (1) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Conversion of preferred stock to common stock (in shares) |  |  | (1) |  |  | 1,136 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Warrant exercises |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  | 263 |  |  |  |  |  |  |  |  | 264 |  | 
| Warrant exercises (in shares) |  |  |  |  |  |  |  |  | 657 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Deemed dividend paid in common stock due to down round provision, recorded in additional paid-in capital |  |  |  |  |  |  |  |  | $ 5 |  |  |  |  |  | (5) |  |  |  |  |  |  |  |  |  |  | 
| Deemed dividend paid in common stock due to down round provision recorded in additional paid-in capital (in share) |  |  |  |  |  |  |  |  | 4,620 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Dividends accrued on Series C and D convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (384) |  |  |  |  |  |  |  |  | (384) |  | 
| Reclassification of warrants from liability to equity classified |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,601 |  |  |  |  |  |  |  |  | 8,601 |  | 
| Stock-based compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 996 |  |  |  |  |  |  |  |  | 996 |  | 
| Reclassification of prior period preferred stock dividends |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (4,265) |  | 4,265 |  |  |  |  |  |  |  |  | 
| Net loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (20,991) |  |  |  |  |  |  | (20,991) |  | 
| Ending balance at Aug. 31, 2022 |  |  |  |  |  |  |  |  | $ 813 |  |  |  |  |  | 687,732 |  | (782,857) |  |  |  |  |  |  | (94,312) |  | 
| Ending balance (shares) at Aug. 31, 2022 |  |  |  | 34 |  |  |  |  | 812,698 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at May. 31, 2022 |  |  |  |  |  |  |  |  | $ 720 |  |  |  |  |  | 671,013 |  | (766,131) |  |  |  |  |  |  | (94,398) |  | 
| Beginning balance (shares) at May. 31, 2022 |  |  |  | 35 |  |  |  |  | 720,028 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Loss on induced conversion |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 638 |  | 
| Warrant exercises (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 500 |  | 
| Net loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (47,486) |  | 
| Ending balance at Nov. 30, 2022 |  |  |  |  |  |  |  |  | $ 825 |  |  |  |  |  | 692,558 |  | (809,352) |  |  |  |  |  |  | (115,969) |  | 
| Ending balance (shares) at Nov. 30, 2022 |  |  |  | 34 |  |  |  |  | 825,279 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Beginning balance at Aug. 31, 2022 |  |  |  |  |  |  |  |  | $ 813 |  |  |  |  |  | 687,732 |  | (782,857) |  |  |  |  |  |  | (94,312) |  | 
| Beginning balance (shares) at Aug. 31, 2022 |  |  |  | 34 |  |  |  |  | 812,698 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Issuance of stock for convertible note repayment |  |  |  |  |  |  |  |  | $ 2 |  |  |  |  |  | 498 |  |  |  |  |  |  |  |  | 500 |  | 
| Issuance of stock for convertible note repayment (in shares) |  |  |  |  |  |  |  |  | 1,822 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Loss on induced conversion |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 638 |  |  |  |  |  |  |  |  | 638 |  | 
| Stock issued for compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 310 |  |  |  |  |  |  |  |  | 310 |  | 
| Stock issued for compensation (in shares) |  |  |  |  |  |  |  |  | 765 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Exercise of warrants, net of offering costs |  |  |  |  |  |  |  |  | $ 10 |  |  |  |  |  | 2,123 |  |  |  |  |  |  |  |  | 2,133 |  | 
| Exercise of warrants, net of offering costs (in shares) |  |  |  |  |  |  |  |  | 9,652 |  |  |  |  |  |  |  |  |  |  | 9,700 |  |  |  |  |  | 
| Make-whole shares related to private warrant exchange (in shares) |  |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Dividend paid in common stock upon conversion of Series C convertible preferred stock ($0.50 per share) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 159 |  |  |  |  |  |  |  |  | 159 |  | 
| Dividend paid in common stock upon conversion of Series C convertible preferred stock ($0.50 per share) (in shares) |  |  |  |  |  |  |  |  | 319 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| Dividends accrued on Series C and D convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (369) |  |  |  |  |  |  |  |  | (369) |  | 
| Stock-based compensation |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,467 |  |  |  |  |  |  |  |  | 1,467 |  | 
| Net loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (26,495) |  |  |  |  |  |  | (26,495) |  | 
| Ending balance at Nov. 30, 2022 |  |  |  |  |  |  |  |  | $ 825 |  |  |  |  |  | $ 692,558 |  | $ (809,352) |  |  |  |  |  |  | $ (115,969) |  | 
| Ending balance (shares) at Nov. 30, 2022 |  |  |  | 34 |  |  |  |  | 825,279 | 443 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 
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