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Debt Security Investments (Details 1) (U.S. Treasury Securities [Member], USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
U.S. Treasury Securities [Member]
   
Gross unrealized losses and fair value of all available for sale debt security investments    
Fair value, Less than 12 months $ 47,235 $ 36,944
Fair value, 12 months or more      
Fair value 47,235 36,944
Unrealized losses, Less than 12 months (8) (6)
Unrealized losses, 12 months or more      
Unrealized losses $ (8) $ (6)