FAIR VALUE MEASUREMENTS AND FINANCIAL INSTRUMENTS - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Fair Value on a Recurring Basis - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Total	$ 1,224,779	$ 1,167,397
Liabilities:
Contingent consideration arrangements	(1,965)	(2,647)
Money market funds
Assets:
Cash equivalents:	762,064	780,425
Time deposits
Assets:
Cash equivalents:	85,038	60,000
Treasury discount notes
Assets:
Cash equivalents:	149,908	100,457
Commercial paper
Assets:
Cash equivalents:	217,342	215,325
Certificates of deposit
Assets:
Cash equivalents:	4,797	6,195
Commercial paper
Assets:
Marketable securities:	4,990	4,995
Equity security with a readily determinable fair value
Assets:
Marketable securities:	640
Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total	912,612	880,882
Liabilities:
Contingent consideration arrangements	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents:	762,064	780,425
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Assets:
Cash equivalents:	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury discount notes
Assets:
Cash equivalents:	149,908	100,457
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Commercial paper
Assets:
Cash equivalents:	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit
Assets:
Cash equivalents:	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Commercial paper
Assets:
Marketable securities:	0	0
Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Equity security with a readily determinable fair value
Assets:
Marketable securities:	640
Significant Other Observable Inputs (Level 2)
Assets:
Total	312,167	286,515
Liabilities:
Contingent consideration arrangements	0	0
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:	85,038	60,000
Significant Other Observable Inputs (Level 2) | Treasury discount notes
Assets:
Cash equivalents:	0	0
Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Cash equivalents:	217,342	215,325
Significant Other Observable Inputs (Level 2) | Certificates of deposit
Assets:
Cash equivalents:	4,797	6,195
Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Marketable securities:	4,990	4,995
Significant Other Observable Inputs (Level 2) | Equity security with a readily determinable fair value
Assets:
Marketable securities:	0
Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Liabilities:
Contingent consideration arrangements	(1,965)	(2,647)
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
Significant Unobservable Inputs (Level 3) | Treasury discount notes
Assets:
Cash equivalents:	0	0
Significant Unobservable Inputs (Level 3) | Commercial paper
Assets:
Cash equivalents:	0	0
Significant Unobservable Inputs (Level 3) | Certificates of deposit
Assets:
Cash equivalents:	0	0
Significant Unobservable Inputs (Level 3) | Commercial paper
Assets:
Marketable securities:	0	$ 0
Significant Unobservable Inputs (Level 3) | Equity security with a readily determinable fair value
Assets:
Marketable securities:	$ 0