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Concentrations of Credit and Other Risks (Tables)
 12 Months Ended
Dec. 31, 2012
Concentrations of Credit and Other Risks [Abstract]  
Product revenue by geographic destination as a percentage of total product revenues

Product revenue by geographic destination as a percentage of total product revenues were as follows for the years ended December 31:
 
   
2012
  
2011
  
2010
 
           
Domestic
  84%  84%  85%
Foreign
  16   16   15