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Investments and Fair Value Measurement (Details) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of available-for-sale securities    
Amortized Cost $ 75,672 $ 82,612
Gross Unrealized Gains 15 19
Gross Unrealized (Losses)    (7)
Estimated Fair Value 75,687 82,624
Cash equivalents [Member]
   
Schedule of available-for-sale securities    
Amortized Cost 13,595 15,258
Gross Unrealized Gains      
Gross Unrealized (Losses)      
Estimated Fair Value 13,595 15,258
Marketable securities [Member]
   
Schedule of available-for-sale securities    
Amortized Cost 62,077 67,354
Gross Unrealized Gains 15 19
Gross Unrealized (Losses)    (7)
Estimated Fair Value 62,092 67,366
Money market funds [Member] | Cash equivalents [Member]
   
Schedule of available-for-sale securities    
Amortized Cost 13,595 15,258
Gross Unrealized Gains      
Gross Unrealized (Losses)      
Estimated Fair Value 13,595 15,258
U.S. government sponsored entity debt securities [Member] | Marketable securities [Member]
   
Schedule of available-for-sale securities    
Amortized Cost 42,732 27,020
Gross Unrealized Gains 15  
Gross Unrealized (Losses)    (7)
Estimated Fair Value 42,747 27,013
U.S. treasury debt securities [Member] | Marketable securities [Member]
   
Schedule of available-for-sale securities    
Amortized Cost   751
Gross Unrealized Gains   1
Gross Unrealized (Losses)     
Estimated Fair Value   752
Corporate debt securities [Member] | Marketable securities [Member]
   
Schedule of available-for-sale securities    
Amortized Cost 19,345 39,583
Gross Unrealized Gains    18
Gross Unrealized (Losses)     
Estimated Fair Value $ 19,345 $ 39,601