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Fair Value of Financial Instruments (Tables)
9 Months Ended
Sep. 30, 2012
Fair Value of Financial Instruments [Abstract]  
Fair Value of long-term debt
The fair value of our long-term debt is estimated based upon quoted market prices at the reporting date for those financial instruments.

 
September 30, 2012
 
December 31, 2011
 
Carrying
     
Carrying
   
($ in thousands)
Amount
 
Fair Value
 
Amount
 
Fair Value
               
Long-term debt
$ 8,257,599
 
$ 8,650,919
 
$ 8,205,841
 
$ 7,958,873