FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets:
Marketable securities:	$ 151,549	$ 165,695
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total Assets	392,471	400,672
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Treasury and government agency money market funds
Assets:
Cash equivalents:	284,629	321,314
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Assets:
Marketable securities:		4,667
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Long-term marketable equity securities
Assets:
Long-term investments:	107,842	74,691
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Total Assets	333,162	403,720
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Cash equivalents:	176,963	237,942
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents:	4,650	4,750
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets:
Marketable securities:	39,044	48,705
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | States of the U.S. and state political subdivisions
Assets:
Marketable securities:	112,505	112,323
Fair value on a recurring basis | Significant Unobservable Inputs (Level 3)
Assets:
Total Assets	7,720	5,870
Liabilities:
Contingent consideration arrangement		(10,000)
Fair value on a recurring basis | Significant Unobservable Inputs (Level 3) | Auction rate securities
Assets:
Long-term investments:	7,720	5,870
Fair value on a recurring basis | Total Fair Value Measurements
Assets:
Total Assets	733,353	810,262
Liabilities:
Contingent consideration arrangement		(10,000)
Fair value on a recurring basis | Total Fair Value Measurements | Treasury and government agency money market funds
Assets:
Cash equivalents:	284,629	321,314
Fair value on a recurring basis | Total Fair Value Measurements | Commercial paper
Assets:
Cash equivalents:	176,963	237,942
Fair value on a recurring basis | Total Fair Value Measurements | Time deposits
Assets:
Cash equivalents:	4,650	4,750
Fair value on a recurring basis | Total Fair Value Measurements | Corporate debt securities
Assets:
Marketable securities:	39,044	48,705
Fair value on a recurring basis | Total Fair Value Measurements | States of the U.S. and state political subdivisions
Assets:
Marketable securities:	112,505	112,323
Fair value on a recurring basis | Total Fair Value Measurements | Equity securities
Assets:
Marketable securities:		4,667
Fair value on a recurring basis | Total Fair Value Measurements | Auction rate securities
Assets:
Long-term investments:	7,720	5,870
Fair value on a recurring basis | Total Fair Value Measurements | Long-term marketable equity securities
Assets:
Long-term investments:	$ 107,842	$ 74,691