FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Marketable securities:	$ 138,597	$ 165,695
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total Assets	404,590	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:	304,695	321,314
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Money market funds
Assets:
Cash equivalents:	7,848
Fair value on a recurring basis | Quoted Market Prices in Active Markets for Identical Assets (Level 1) | Equity security
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:	92,047	74,691
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Total Assets	434,574	403,720
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets:
Cash equivalents:	291,427	237,942
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Time deposits
Assets:
Cash equivalents:	4,550	4,750
Fair value on a recurring basis | Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets:
Marketable securities:	26,476	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:	112,121	112,323
Fair value on a recurring basis | Significant Unobservable Inputs (Level 3)
Assets:
Total Assets	6,730	5,870
Liabilities:
Contingent consideration arrangement		(10,000)
Fair value on a recurring basis | Significant Unobservable Inputs (Level 3) | Auction rate security
Assets:
Long-term investments:	6,730	5,870
Fair value on a recurring basis | Total Fair Value Measurements
Assets:
Total Assets	845,894	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:	304,695	321,314
Fair value on a recurring basis | Total Fair Value Measurements | Money market funds
Assets:
Cash equivalents:	7,848
Fair value on a recurring basis | Total Fair Value Measurements | Commercial paper
Assets:
Cash equivalents:	291,427	237,942
Fair value on a recurring basis | Total Fair Value Measurements | Time deposits
Assets:
Cash equivalents:	4,550	4,750
Fair value on a recurring basis | Total Fair Value Measurements | Corporate debt securities
Assets:
Marketable securities:	26,476	48,705
Fair value on a recurring basis | Total Fair Value Measurements | States of the U.S. and state political subdivisions
Assets:
Marketable securities:	112,121	112,323
Fair value on a recurring basis | Total Fair Value Measurements | Equity security
Assets:
Marketable securities:		4,667
Fair value on a recurring basis | Total Fair Value Measurements | Auction rate security
Assets:
Long-term investments:	6,730	5,870
Fair value on a recurring basis | Total Fair Value Measurements | Long-term marketable equity securities
Assets:
Long-term investments:	$ 92,047	$ 74,691