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STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | May 31, 2021 | Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options outstanding | 10,357,133 |  |  | 11,065,658
Reserved shares of common stock for issuance ( in shares) | 46,183,689 |  |  |
Options granted, weighted-average grant date fair value (in dollars per share) | $ 16.84 |  |  |
Options granted (in shares) | 709,448 | 2,354,515 |  |
Options exercised, intrinsic value | $ 47.6 | $ 0.1 |  |
Remaining unrecognized stock-based compensation expense | $ 17.9 |  |  |
2009 Equity Incentive Plan |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Options outstanding | 9,647,780 |  |  |
Reserved shares of common stock for issuance ( in shares) | 0 |  |  |
2021 Equity Incentive Plan |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Reserved shares of common stock for issuance ( in shares) |  |  | 23,722,254 |
Outstanding stock options |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Exercise price as a percentage of fair value | 100.00% |  |  |
Exercise price as a percentage of fair value for shareholders owning specified minimum amount | 110.00% |  |  |
Significant shareholder threshold used for determining exercise price | 10.00% |  |  |
Exercise period | 10 years |  |  |
Weighted average period for recognition of stock-based compensation expense | 3 years 7 months 6 days |  |  |
Outstanding stock options | Share-based Payment Arrangement, Tranche One |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period | 1 year |  |  |
Vesting percentage | 25.00% |  |  |
Outstanding stock options | Share-based Payment Arrangement, Tranche Two |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Vesting period | 3 years |  |  |
Vesting percentage | 2.08% |  |  |

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