FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Level 1
Fair value of certain assets
Cash	$ 218,121	$ 139,300
Assets measured at fair value	352,399	199,402
Level 1 | Money market funds
Fair value of certain assets
Assets measured at fair value	134,278	60,102
Level 2
Fair value of certain assets
Foreign currency derivatives	38
Assets measured at fair value	513,522	407,802
Level 2 | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	6,007	22,045
Level 2 | Commercial paper
Fair value of certain assets
Assets measured at fair value	9,996	5,991
Level 2 | Municipal securities
Fair value of certain assets
Assets measured at fair value	497,481	379,766
Level 3
Fair value of certain assets
Assets measured at fair value	13,813	17,276
Level 3 | Auction rate securities
Fair value of certain assets
Assets measured at fair value	12,819	16,184
Level 3 | Put option related to auction rate securities
Fair value of certain assets
Assets measured at fair value	994	1,092
Total fair value
Fair value of certain assets
Cash	218,121	139,300
Foreign currency derivatives	38
Assets measured at fair value	879,734	624,480
Total fair value | Money market funds
Fair value of certain assets
Assets measured at fair value	134,278	60,102
Total fair value | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	6,007	22,045
Total fair value | Commercial paper
Fair value of certain assets
Assets measured at fair value	9,996	5,991
Total fair value | Municipal securities
Fair value of certain assets
Assets measured at fair value	497,481	379,766
Total fair value | Auction rate securities
Fair value of certain assets
Assets measured at fair value	12,819	16,184
Total fair value | Put option related to auction rate securities
Fair value of certain assets
Assets measured at fair value	$ 994	$ 1,092