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Asset Retirement Obligation (Tables)
 12 Months Ended
Dec. 31, 2011
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,
 
2011
 
2010
Liability at January 1,
$
7,181

 
$
6,688

Accretion expense
493

 
518

Liabilities incurred
486

 
76

Liabilities settled
(1,970
)
 
(35
)
Revisions to cash flows
102

 
(66
)
Liability at December 31,
$
6,292

 
$
7,181