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Fair Value Measurements (Tables)
6 Months Ended
Jun. 30, 2012
Fair Value Disclosures [Abstract]  
Carrying value and fair value of variable rate long-term debt
 
As of June 30, 2012
 
As of December 31, 2011
 
Carrying
Value
 
Fair
Value
 
Carrying
Value
 
Fair
Value
Variable-rate long-term debt
$
608,203

 
$
608,203

 
$
573,984

 
$
573,984