FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Marketable securities	$ 49,912	$ 19,993
Other non-current assets	318,832	301,441
Total assets	2,256,611	2,550,995
Liabilities:
Contingent consideration arrangement	(636)	(6,918)
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total assets	2,007,519	2,164,576
Liabilities:
Contingent consideration arrangement	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Total assets	242,603	377,924
Liabilities:
Contingent consideration arrangement	0	0
Significant Unobservable Inputs (Level 3)
Assets:
Total assets	6,489	8,495
Liabilities:
Contingent consideration arrangement	(636)	(6,918)
Money market funds
Assets:
Cash equivalents	2,007,519	2,164,576
Money market funds | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	2,007,519	2,164,576
Money market funds | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	0	0
Money market funds | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Treasury discount notes
Assets:
Cash equivalents	99,882	199,896
Marketable securities	49,912
Treasury discount notes | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	0	0
Marketable securities	0
Treasury discount notes | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	99,882	199,896
Marketable securities	49,912
Treasury discount notes | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Marketable securities	0
Time deposits
Assets:
Cash equivalents	72,809	128,075
Time deposits | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents	0	0
Time deposits | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	72,809	128,075
Time deposits | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0	0
Short-term investments
Assets:
Short-term investments	20,000
Short-term investments | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Short-term investments	0
Short-term investments | Significant Other Observable Inputs (Level 2)
Assets:
Short-term investments	20,000
Short-term investments | Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments	0
Commercial paper
Assets:
Cash equivalents		29,960
Marketable securities		19,993
Commercial paper | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash equivalents		0
Marketable securities		0
Commercial paper | Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents		29,960
Marketable securities		19,993
Commercial paper | Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents		0
Marketable securities		0
Warrant
Assets:
Other non-current assets	6,489	8,495
Warrant | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Other non-current assets	0	0
Warrant | Significant Other Observable Inputs (Level 2)
Assets:
Other non-current assets	0	0
Warrant | Significant Unobservable Inputs (Level 3)
Assets:
Other non-current assets	$ 6,489	$ 8,495