STOCKHOLDERS’ EQUITY (DEFICIT) - Reserve Shares of Common Stock (Details) - shares |
Mar. 31, 2021 |
Dec. 31, 2020 |
|---|---|---|
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 54,447,630 | 66,167,171 |
| Outstanding stock options | ||
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 20,588,121 | 17,641,380 |
| Warrants to purchase common stock | ||
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 27,093,465 | 38,727,616 |
| Restricted stock units subject to vesting | ||
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 203,667 | 203,667 |
| Shares issuable upon conversion of convertible debt | ||
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 0 | 18,057 |
| For possible future issuance under the Omnibus Plan | ||
| Class of Stock [Line Items] | ||
| Capital shares reserved for future issuance (in shares) | 6,562,377 | 9,576,451 |