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Asset Retirement Obligation (Tables)
 12 Months Ended
Dec. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Change in Asset Retirement Obligation
The following table presents the change in our gross conditional ARO (in thousands):

 
December 31,
 
2012
 
2011
Liability at January 1,
$
6,292

 
$
7,181

Accretion expense
473

 
493

Liabilities incurred
2,466

 
486

Liabilities settled
(35
)
 
(1,970
)
Revisions to cash flows
87

 
102

Liability at December 31,
$
9,283

 
$
6,292