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Fair Value Measurements (Tables)
6 Months Ended
Jun. 30, 2011
Fair Value Measurements [Abstract]  
Carrying value and fair value of variable rate long-term debt
                                 
    As of June 30, 2011     As of December 31, 2010  
    Carrying     Fair     Carrying     Fair  
    Value     Value     Value     Value  
Variable-rate long-term debt
  $ 481,250     $ 483,055     $ 493,750     $ 496,219