FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Marketable debt securities		$ 49,995
Total	$ 653,610	751,725
Treasury discount notes
Assets:
Marketable debt securities	0	49,995
Money market funds
Assets:
Cash equivalents	552,024	374,014
Treasury discount notes
Assets:
Cash equivalents	100,000	324,995
Time deposits
Assets:
Cash equivalents	1,586	2,721
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	552,024	374,014
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury discount notes
Assets:
Marketable debt securities	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents	552,024	374,014
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury discount notes
Assets:
Cash equivalents	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Assets:
Cash equivalents	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Total	101,586	377,711
Significant Other Observable Inputs (Level 2) | Treasury discount notes
Assets:
Marketable debt securities	0	49,995
Significant Other Observable Inputs (Level 2) | Money market funds
Assets:
Cash equivalents	0	0
Significant Other Observable Inputs (Level 2) | Treasury discount notes
Assets:
Cash equivalents	100,000	324,995
Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents	1,586	2,721
Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Significant Unobservable Inputs (Level 3) | Treasury discount notes
Assets:
Marketable debt securities	0	0
Significant Unobservable Inputs (Level 3) | Money market funds
Assets:
Cash equivalents	0	0
Significant Unobservable Inputs (Level 3) | Treasury discount notes
Assets:
Cash equivalents	0	0
Significant Unobservable Inputs (Level 3) | Time deposits
Assets:
Cash equivalents	$ 0	$ 0