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Fair Value of Financial Instruments (Tables)
12 Months Ended
Dec. 31, 2011
Fair Value of Financial Instruments [Abstract]  
Carrying value and fair value of variable rate long-term debt
                                 
    As of December 31,  
    2011     2010  
    Carrying
Value
    Fair
Value
    Carrying
Value
    Fair
Value
 

Variable-rate long-term debt

  $ 573,984     $ 573,984     $ 493,750     $ 496,219