FAIR VALUE MEASUREMENTS - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 630,012	$ 131,627
Short-term investments	99,996	514,461
Fair Value, Measurements, Recurring [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	466,233	12,355
Short-term investments	99,996	514,461
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	466,233	12,355
Short-term investments	$ 99,996	$ 514,461