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Fair Value of Financial Instruments (Details2) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Fair value hierarchy for its financial assets    
Available-for-sale securities $ 39,297 $ 17,950
Fair Value
   
Fair value hierarchy for its financial assets    
Money market funds 1,445 2,792
Total assets 44,769 20,742
Fair Value | Certificates of deposit
   
Fair value hierarchy for its financial assets    
Available-for-sale securities 5,400  
Fair Value | Corporate notes and commercial paper
   
Fair value hierarchy for its financial assets    
Available-for-sale securities 20,019  
Fair Value | Corporate notes
   
Fair value hierarchy for its financial assets    
Available-for-sale securities   7,393
Fair Value | U.S. government debt securities
   
Fair value hierarchy for its financial assets    
Available-for-sale securities 17,905 10,557
Level 1
   
Fair value hierarchy for its financial assets    
Money market funds 1,445 2,792
Total assets 1,445 2,792
Level 2
   
Fair value hierarchy for its financial assets    
Total assets 43,324 17,950
Level 2 | Certificates of deposit
   
Fair value hierarchy for its financial assets    
Available-for-sale securities 5,400  
Level 2 | Corporate notes and commercial paper
   
Fair value hierarchy for its financial assets    
Available-for-sale securities 20,019  
Level 2 | Corporate notes
   
Fair value hierarchy for its financial assets    
Available-for-sale securities   7,393
Level 2 | U.S. government debt securities
   
Fair value hierarchy for its financial assets    
Available-for-sale securities $ 17,905 $ 10,557