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Financial Instruments (Details Textual) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Derivative
Dec. 31, 2010
Derivative
Financial Instruments (Textual) [Abstract]      
Financial instruments including money market funds maturities period 90 days    
Maximum maturities period of long-term marketable securities 3 years    
Minimum maturities period of long-term marketable securities 1 year    
Maximum maturities period of short-term marketable securities 12 months    
Minimum maturities period of short-term marketable securities 90 days    
Sales of marketable securities $ 0 $ 0 $ 0
Total fair value of marketable securities 200,000,000    
Total gross unrealized loss position 200,000    
Recognize impairment charges 0 0 0
Investments in marketable securities 0 0  
Net realized and unrealized loss related to forward contracts 700,000    
Redeemable noncontrolling interest (note 14) $ 0 $ 3,863,000  
Derivative Number of Instruments Entered into or Settled During Period   0 0