STOCKHOLDERS' EQUITY - Awards granted in 2020 (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| STOCKHOLDERS' EQUITY | |||
| Number of days for settlement | 30 days | ||
| General and administrative: other | |||
| STOCKHOLDERS' EQUITY | |||
| Stock-based compensation expense | $ 25.4 | $ 4.4 | $ 14.9 |
| Performance Vesting | |||
| STOCKHOLDERS' EQUITY | |||
| Stock-based compensation expense | 5.8 | ||
| Performance Vesting | General and administrative: other | |||
| STOCKHOLDERS' EQUITY | |||
| Stock-based compensation expense | $ 1.2 | $ (5.8) | $ 5.8 |