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FAIR VALUE OF CERTAIN FINANCIAL ASSETS AND LIABILITIES (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Put options related to auction rate securities
   
Fair value of certain assets    
Assets measured at fair value $ 3,000  
Level 1
   
Fair value of certain assets    
Cash 81,879 50,202
Assets measured at fair value 319,942 377,724
Level 1 | Money market funds
   
Fair value of certain assets    
Assets measured at fair value 230,029 242,001
Level 1 | U.S. Treasuries
   
Fair value of certain assets    
Assets measured at fair value 8,034 85,521
Level 2
   
Fair value of certain assets    
Assets measured at fair value 438,013 197,704
Level 2 | Certificates of deposit
   
Fair value of certain assets    
Assets measured at fair value 69,078 40,010
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 291,984 81,899
Level 2 | U.S. government agency securities.
   
Fair value of certain assets    
Assets measured at fair value 16,005 19,688
Level 2 | Variable rate demand notes
   
Fair value of certain assets    
Assets measured at fair value 58,924 56,107
Level 3
   
Fair value of certain assets    
Assets measured at fair value 38,893 72,020
Level 3 | Auction rate securities
   
Fair value of certain assets    
Assets measured at fair value 35,852 68,252
Level 3 | Put options related to auction rate securities
   
Fair value of certain assets    
Assets measured at fair value 3,041 3,768
Total fair value
   
Fair value of certain assets    
Cash 81,879 50,202
Assets measured at fair value 796,848 647,448
Total fair value | Money market funds
   
Fair value of certain assets    
Assets measured at fair value 230,029 242,001
Total fair value | U.S. Treasuries
   
Fair value of certain assets    
Assets measured at fair value 8,034 85,521
Total fair value | Certificates of deposit
   
Fair value of certain assets    
Assets measured at fair value 69,078 40,010
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 291,984 81,899
Total fair value | U.S. government agency securities.
   
Fair value of certain assets    
Assets measured at fair value 16,005 19,688
Total fair value | Variable rate demand notes
   
Fair value of certain assets    
Assets measured at fair value 58,924 56,107
Total fair value | Auction rate securities
   
Fair value of certain assets    
Assets measured at fair value 35,852 68,252
Total fair value | Put options related to auction rate securities
   
Fair value of certain assets    
Assets measured at fair value $ 3,041 $ 3,768