FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Cash equivalents	$ 333,986	$ 314,850
Money market funds
Assets:
Cash equivalents	156,063	291,810
Treasury discount notes
Assets:
Cash equivalents	174,987
Time deposits
Assets:
Cash equivalents	2,936	23,040
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	156,063	291,810
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents	156,063	291,810
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury discount notes
Assets:
Cash equivalents	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:
Cash equivalents	177,923	23,040
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	174,987
Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents	2,936	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) | Treasury discount notes
Assets:
Cash equivalents	0
Significant Unobservable Inputs (Level 3) | Time deposits
Assets:
Cash equivalents	$ 0	$ 0