INCOME TAXES - Unrecognized tax benefits (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] | |||
| Unrecognized tax benefits as of the beginning of the year | $ 5,033 | $ 2,433 | $ 862 |
| Increases related to prior year tax provisions | 182 | 383 | 197 |
| Decrease related to prior year tax provisions | (888) | (247) | |
| Increase related to current year tax provisions | 1,812 | 2,464 | 1,374 |
| Unrecognized tax benefits as of the end of the year | $ 6,139 | $ 5,033 | $ 2,433 |