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Fair Value Measurements (Tables)
9 Months Ended
Sep. 30, 2011
Fair Value Measurements [Abstract] 
Carrying value and fair value of variable rate long-term debt
                                 
    As of September 30, 2011     As of December 31, 2010  
    Carrying
Value
    Fair
Value
    Carrying
Value
    Fair
Value
 
         

Variable-rate long-term debt

  $     581,250     $     579,797     $     493,750     $     496,219