FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Assets:
Marketable debt securities	$ 0	$ 49,995,000
Total	314,040,000	751,725,000
Treasury discount notes
Assets:
Marketable debt securities		49,995,000
Money market funds
Assets:
Cash equivalents	314,040,000	374,014,000
Treasury discount notes
Assets:
Cash equivalents		324,995,000
Time deposits
Assets:
Cash equivalents		2,721,000
Quoted Market Prices for Identical Assets in Active Markets (Level 1)
Assets:
Total	314,040,000	374,014,000
Quoted Market Prices for Identical Assets in Active Markets (Level 1) | Treasury discount notes
Assets:
Marketable debt securities		0
Quoted Market Prices for Identical Assets in Active Markets (Level 1) | Money market funds
Assets:
Cash equivalents	314,040,000	374,014,000
Quoted Market Prices for Identical Assets in Active Markets (Level 1) | Treasury discount notes
Assets:
Cash equivalents		0
Quoted Market Prices for Identical Assets in Active Markets (Level 1) | Time deposits
Assets:
Cash equivalents		0
Significant Other Observable Inputs (Level 2)
Assets:
Total	0	377,711,000
Significant Other Observable Inputs (Level 2) | Treasury discount notes
Assets:
Marketable debt securities		49,995,000
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		324,995,000
Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents		2,721,000
Significant Unobservable Inputs (Level 3)
Assets:
Total	0	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