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Asset Retirement Obligation (Tables)
12 Months Ended
Dec. 31, 2012
Information Related to Asset Retirement Obligation

The following table reflects information related to our asset retirement obligations:

 

Balance at December 31, 2010

   $ 173,673   

Additions to asset retirement obligations

     708   

Accretion expense

     10,573   

Liabilities settled

     (4,292
  

 

 

 

Balance at December 31, 2011

     180,662   

Additions to asset retirement obligations

     5,434   

Accretion expense

     10,871   

Liabilities settled

     (7,308
  

 

 

 

Balance at December 31, 2012

   $ 189,659