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Asset Retirement Obligations (Details) (Predecessors [Member], USD $)
In Thousands, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Predecessors [Member]
   
Schedule of change in asset retirement obligation    
Asset retirement obligations at beginning of period $ 11,733 $ 7,150
Liabilities incurred 75 44
Liabilities settled (98)  
Accretion 420 322
Divestitures      
Asset retirement obligations at end of period $ 12,130 $ 7,516