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STOCKHOLDERS' EQUITY - EQUITY PLANS - SCHEDULE OF AGGREGATE OPTION AND AWARD ACTIVITY (Parenthetical) (Details) - shares | Feb. 28, 2021 | Dec. 31, 2020 | Dec. 31, 2019
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STOCKHOLDERS' EQUITY |  |  |
Outstanding Stock Options (in shares) |  | 43,663,691 | 37,614,013
Common stock, shares reserved for future issuance |  | 118,156,885 |
2018 Inducement Award Plan |  |  |
STOCKHOLDERS' EQUITY |  |  |
Common stock, shares reserved for future issuance |  | 9,300,000 |
Subsequent Event | 2018 Inducement Award Plan |  |  |
STOCKHOLDERS' EQUITY |  |  |
Common stock, shares reserved for future issuance | 10,100,000 |  |
Performance-Based Stock Options |  |  |
STOCKHOLDERS' EQUITY |  |  |
Outstanding Stock Options (in shares) |  | 5,500,000 |

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