FINANCIAL INSTRUMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Cash equivalents	$ 344,001	$ 197,615
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	294,001	147,615
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	50,000	50,000
Money market funds
Assets:
Cash equivalents	294,001	147,615
Money market funds | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	294,001	147,615
Money market funds | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Time deposits
Assets:
Cash equivalents	50,000	50,000
Time deposits | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	0	0
Time deposits | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	$ 50,000	$ 50,000