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Summary of Significant Accounting Policies (Details 4) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Short-term and long-term investments      
Amortized Cost $ 201,149 $ 284,489  
Gross Unrealized Gains 34 253  
Gross Unrealized Losses (280) (238)  
Estimated Fair Value 200,903 284,504 230,445
Amortized Cost      
Maturity dates, investments, 2012 193,147    
Maturity dates, investments, 2013 8,002    
Total, Amortized Cost 201,149    
Estimated Fair Value      
Maturity dates, investments, 2012 192,947    
Maturity dates, investments, 2013 7,956    
Total, Estimated Fair Value 200,903 284,504 230,445
U.S. Government and agency securities
     
Short-term and long-term investments      
Amortized Cost 697 2,178  
Gross Unrealized Gains   1  
Estimated Fair Value 697 2,179  
Estimated Fair Value      
Total, Estimated Fair Value 697 2,179  
Obligations of government-sponsored enterprises
     
Short-term and long-term investments      
Amortized Cost 8,293 10,142  
Gross Unrealized Gains 3 7  
Gross Unrealized Losses (3) (11)  
Estimated Fair Value 8,293 10,138  
Estimated Fair Value      
Total, Estimated Fair Value 8,293 10,138  
Corporate debt securities
     
Short-term and long-term investments      
Amortized Cost 192,059 268,739  
Gross Unrealized Gains 31 245  
Gross Unrealized Losses (277) (215)  
Estimated Fair Value 191,813 268,769  
Estimated Fair Value      
Total, Estimated Fair Value 191,813 268,769  
Certificates of deposit
     
Short-term and long-term investments      
Amortized Cost 100 750  
Estimated Fair Value 100 750  
Estimated Fair Value      
Total, Estimated Fair Value 100 750  
Taxable municipal bonds
     
Short-term and long-term investments      
Amortized Cost   2,680  
Gross Unrealized Losses   (12)  
Estimated Fair Value   2,668  
Estimated Fair Value      
Total, Estimated Fair Value   $ 2,668