FAIR VALUE OF FINANCIAL INSTRUMENTS - Investments Valued Under the Measurement Alternative (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | |
|---|---|---|---|
Mar. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Equity Securities without Readily Determinable Fair Value [Roll Forward] | |||
| Beginning balance, before cumulative impairment | $ 3,305 | $ 11,205 | |
| Accumulated impairment as of January 1, | 0 | $ 0 | |
| Beginning balance, after cumulative impairment | $ 3,305 | 11,205 | |
| Removal of investment in connection with step acquisition | 0 | (9,700) | |
| Acquisition of interest in a privately held company | 0 | 1,800 | |
| Ending period balance | $ 3,305 | $ 3,305 |