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FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details) (USD $)
Dec. 31, 2012
Dec. 31, 2011
Fair value disclosure    
Short-term investments $ 29,054,000 $ 33,960,000
Restricted cash equivalents and short-term investments 9,658,000 52,693,000
Concentrations of Credit Risk of Financial Instruments    
Cash, cash equivalents, and certificates of deposit which are not FDIC-insured 53,800,000 98,800,000
Fair value disclosure
   
Fair value disclosure    
Cash and cash equivalents 90,702,000 141,295,000
Restricted cash equivalents and short-term investments 9,658,000 52,693,000
Fair value disclosure | Cash deposits
   
Fair value disclosure    
Cash and cash equivalents 48,293,000 98,258,000
Restricted cash equivalents and short-term investments 5,901,000 11,842,000
Fair value disclosure | Variable rate demand notes
   
Fair value disclosure    
Cash and cash equivalents 29,807,000 29,735,000
Fair value disclosure | Money market funds
   
Fair value disclosure    
Cash and cash equivalents 12,602,000 13,302,000
Restricted cash equivalents and short-term investments   5,375,000
Fair value disclosure | Certificates of deposit
   
Fair value disclosure    
Short-term investments 29,054,000 33,960,000
Restricted cash equivalents and short-term investments $ 3,757,000 $ 35,476,000