FAIR VALUE MEASUREMENT - The liability component was valued based on the Income Approach (Details) - 2021 Notes [Member] - Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2020 $ / shares
Measurement Input, Share Price [Member]
Debt Instrument, Measurement Input	3.63
Measurement Input, Expected Term [Member]
Debt Instrument, Measurement Input	0.87
Measurement Input, Risk Free Interest Rate [Member]
Debt Instrument, Measurement Input	0.10
Measurement Input, Price Volatility [Member]
Debt Instrument, Measurement Input	75.84
Measurement Input, Yield [Member]
Debt Instrument, Measurement Input	10.44