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SHARE-BASED COMPENSATION - Narrative (Details) - USD ($) | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
May 31, 2021 | Jun. 30, 2019 | Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021 | Dec. 31, 2021 | Oct. 01, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Options outstanding (in shares) |  |  | 17,161,000 |  | 17,161,000 |  | 15,703,000 |
Share-based compensation expense |  |  | $ 1,802,000 | $ 1,259,000 | $ 3,696,000 | $ 2,217,000 |  |
Unrecognized compensation cost, non-vested stock options |  |  | $ 8,600,000 |  | $ 8,600,000 |  |  |
Weighted average period unvested stock to be recognized |  |  |  |  | 2 years 4 months 9 days |  |  |
Weighted-average grant-date fair value of stock options granted (in dollars per share) |  |  |  |  | $ 0.46 | $ 2.17 |  |
Exercise of stock options (in shares) |  |  |  |  | 0 |  |  |
Share-based Payment Arrangement, Employee |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Options outstanding (in shares) |  |  | 3,500,000 |  | 3,500,000 |  |  |
Stock options |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares reserved for future issuance (in shares) |  |  | 17,161,000 |  | 17,161,000 |  | 15,703,000 |
Share-based compensation expense |  |  | $ 1,200,000 | $ 1,300,000 | $ 2,500,000 | $ 2,200,000 |  |
Stock options | 2014 Stock Incentive Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of shares reserved for issuance (in shares) | 12,000,000 | 7,900,000 |  |  |  |  |  |
Shares reserved for future issuance (in shares) |  |  | 3,100,000 |  | 3,100,000 |  |  |
Award vesting period |  |  |  |  | 4 years |  |  |
Expected term |  |  |  |  | 10 years |  |  |
Options outstanding (in shares) |  |  | 13,600,000 |  | 13,600,000 |  |  |
Stock options | 2014 Stock Incentive Plan | Vesting on the First Anniversary of Date of Grant |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage of original number of shares subject to the option vesting |  |  |  |  | 25.00% |  |  |
Stock options | 2014 Stock Incentive Plan | Vesting at End of Each Successive Three-Month Period Thereafter |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Percentage of original number of shares subject to the option vesting |  |  |  |  | 6.25% |  |  |
Stock options | Stock Incentive Plan 2009 |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Expected term |  |  |  |  | 10 years |  |  |
Vested stock options outstanding (in shares) |  |  |  |  | 100,000 |  |  |
RSU |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares reserved for future issuance (in shares) |  |  | 8,063,000 |  | 8,063,000 |  | 3,041,000 |
Unrecognized compensation expense |  |  | $ 3,000,000 |  | $ 3,000,000 |  |  |
Share-based compensation expense |  |  | 600,000 |  | $ 1,200,000 | $ 0 |  |
Unvested grant restricted stock units (in shares) |  |  |  |  | 4,161,000 | 0 |  |
RSU | Retention Program |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares received per award (in shares) |  |  |  |  |  |  |  | 1
PSUs |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Unrecognized compensation expense |  |  | 3,000,000 |  | $ 3,000,000 |  |  |
Share-based compensation expense |  |  | 600,000 |  | $ 1,200,000 | $ 0 |  |
Unvested grant restricted stock units (in shares) |  |  |  |  | 1,004,000 | 0 |  |
PSUs | Retention Program |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares received per award (in shares) |  |  |  |  |  |  |  | 1
Percent of base salary |  |  |  |  |  |  |  | 50.00%
Unrecognized compensation expense |  |  | $ 54,000 |  | $ 54,000 |  | $ 87,000 | $ 400,000
Achievement deemed probable, percent |  |  | 20.00% |  | 20.00% |  |  |
Share-based compensation expense |  |  | $ 11,000 |  | $ 33,000 |  |  |

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