FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Level 1
Fair value of certain assets
Cash	$ 147,113	$ 81,879
Assets measured at fair value	211,087	319,942
Level 1 | Money market funds
Fair value of certain assets
Assets measured at fair value	63,974	230,029
Level 1 | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value		8,034
Level 2
Fair value of certain assets
Assets measured at fair value	106,706	438,013
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	5,603	69,078
Level 2 | Corporate bonds
Fair value of certain assets
Assets measured at fair value		2,022
Level 2 | Municipal securities
Fair value of certain assets
Assets measured at fair value	77,038	291,984
Level 2 | U.S. government agency securities.
Fair value of certain assets
Assets measured at fair value		16,005
Level 2 | Variable rate demand notes
Fair value of certain assets
Assets measured at fair value		58,924
Level 3
Fair value of certain assets
Assets measured at fair value	25,085	38,893
Level 3 | Auction rate securities
Fair value of certain assets
Assets measured at fair value	23,156	35,852
Level 3 | Put options related to auction rate securities
Fair value of certain assets
Assets measured at fair value	1,929	3,041
Total fair value
Fair value of certain assets
Cash	147,113	81,879
Assets measured at fair value	342,878	796,848
Total fair value | Money market funds
Fair value of certain assets
Assets measured at fair value	63,974	230,029
Total fair value | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value	24,065	8,034
Total fair value | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	5,603	69,078
Total fair value | Corporate bonds
Fair value of certain assets
Assets measured at fair value		2,022
Total fair value | Municipal securities
Fair value of certain assets
Assets measured at fair value	77,038	291,984
Total fair value | U.S. government agency securities.
Fair value of certain assets
Assets measured at fair value		16,005
Total fair value | Variable rate demand notes
Fair value of certain assets
Assets measured at fair value		58,924
Total fair value | Auction rate securities
Fair value of certain assets
Assets measured at fair value	23,156	35,852
Total fair value | Put options related to auction rate securities
Fair value of certain assets
Assets measured at fair value	$ 1,929	$ 3,041