FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Level 1
Fair value of certain assets
Cash	$ 187,984	$ 147,113
Assets measured at fair value	244,734	211,087
Level 1 | Money market funds
Fair value of certain assets
Assets measured at fair value	56,750	63,974
Level 2
Fair value of certain assets
Assets measured at fair value	350,859	106,706
Level 2 | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value		24,065
Level 2 | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	6,515	5,603
Level 2 | Municipal securities
Fair value of certain assets
Assets measured at fair value	344,344	77,038
Level 3
Fair value of certain assets
Assets measured at fair value	18,242	25,085
Level 3 | Auction rate securities
Fair value of certain assets
Assets measured at fair value	16,723	23,156
Level 3 | Put option related to auction rate securities
Fair value of certain assets
Assets measured at fair value	1,519	1,929
Total fair value
Fair value of certain assets
Cash	187,984	147,113
Assets measured at fair value	613,835	342,878
Total fair value | Money market funds
Fair value of certain assets
Assets measured at fair value	56,750	63,974
Total fair value | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value		24,065
Total fair value | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	6,515	5,603
Total fair value | Municipal securities
Fair value of certain assets
Assets measured at fair value	344,344	77,038
Total fair value | Auction rate securities
Fair value of certain assets
Assets measured at fair value	16,723	23,156
Total fair value | Put option related to auction rate securities
Fair value of certain assets
Assets measured at fair value	$ 1,519	$ 1,929