FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Cash equivalents	$ 309,291	$ 314,850
Money market funds
Assets:
Cash equivalents	306,515	291,810
Time deposits
Assets:
Cash equivalents	2,776	23,040
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	306,515	291,810
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents	306,515	291,810
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:
Cash equivalents	2,776	23,040
Significant Other Observable Inputs (Level 2) | Money market funds
Assets:
Cash equivalents	0	0
Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents	2,776	23,040
Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Significant Unobservable Inputs (Level 3) | Money market funds
Assets:
Cash equivalents	0	0
Significant Unobservable Inputs (Level 3) | Time deposits
Assets:
Cash equivalents	$ 0	$ 0