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Other Long-Term Obligations and Commitments (Details 1) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Reconciliation of the liability for plugging and abandonment costs  
Asset retirement obligation - December 31, 2012 $ 9,012
Liabilities incurred 15
Liabilities settled (23)
Accretion expense 90
Revisions in estimated liabilities 113
Asset retirement obligation - March 31, 2013 $ 9,207