FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Assets:
Cash equivalents		$ 314,850,000
Marketable debt securities	$ 49,992,000	0
Cash equivalents, and marketable securities	796,969,000
Treasury discount notes
Assets:
Marketable debt securities	49,992,000
Money market funds
Assets:
Cash equivalents	269,013,000	291,810,000
Treasury discount notes
Assets:
Cash equivalents	474,976,000
Time deposits
Assets:
Cash equivalents	2,988,000	23,040,000
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents		291,810,000
Cash equivalents, and marketable securities	269,013,000
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury discount notes
Assets:
Marketable debt securities	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents	269,013,000	291,810,000
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		23,040,000
Cash equivalents, and marketable securities	527,956,000
Significant Other Observable Inputs (Level 2) | Treasury discount notes
Assets:
Marketable debt securities	49,992,000
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	474,976,000
Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents	2,988,000	23,040,000
Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents		0
Cash equivalents, and marketable securities	0
Significant Unobservable Inputs (Level 3) | Treasury discount notes
Assets:
Marketable debt securities	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