FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Level 1
Fair value of certain assets
Cash	$ 105,046	$ 50,202
Assets measured at fair value	293,612	377,724
Level 1 | Money market funds
Fair value of certain assets
Assets measured at fair value	142,426	242,001
Level 1 | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value	46,140	85,521
Level 2
Fair value of certain assets
Assets measured at fair value	393,113	197,704
Level 2 | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	68,685	40,010
Level 2 | Corporate bonds
Fair value of certain assets
Assets measured at fair value	2,021
Level 2 | Municipal securities
Fair value of certain assets
Assets measured at fair value	209,583	81,899
Level 2 | U.S. government agency securities.
Fair value of certain assets
Assets measured at fair value	46,013	19,688
Level 2 | Variable rate demand notes
Fair value of certain assets
Assets measured at fair value	66,811	56,107
Level 3
Fair value of certain assets
Assets measured at fair value	42,553	72,020
Level 3 | Auction rate securities
Fair value of certain assets
Assets measured at fair value	39,376	68,252
Level 3 | Put options related to auction rate securities
Fair value of certain assets
Assets measured at fair value	3,177	3,768
Total fair value
Fair value of certain assets
Cash	105,046	50,202
Assets measured at fair value	729,278	647,448
Total fair value | Money market funds
Fair value of certain assets
Assets measured at fair value	142,426	242,001
Total fair value | U.S. Treasuries
Fair value of certain assets
Assets measured at fair value	46,140	85,521
Total fair value | Certificates of deposit
Fair value of certain assets
Assets measured at fair value	68,685	40,010
Total fair value | Corporate bonds
Fair value of certain assets
Assets measured at fair value	2,021
Total fair value | Municipal securities
Fair value of certain assets
Assets measured at fair value	209,583	81,899
Total fair value | U.S. government agency securities.
Fair value of certain assets
Assets measured at fair value	46,013	19,688
Total fair value | Variable rate demand notes
Fair value of certain assets
Assets measured at fair value	66,811	56,107
Total fair value | Auction rate securities
Fair value of certain assets
Assets measured at fair value	39,376	68,252
Total fair value | Put options related to auction rate securities
Fair value of certain assets
Assets measured at fair value	3,177	3,768
Put options related to auction rate securities
Fair value of certain assets
Assets measured at fair value	$ 3,200