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Other Long-Term Obligations and Commitments (Details 1) (USD $)
In Thousands, unless otherwise specified
9 Months Ended
Sep. 30, 2012
Reconciliation of the liability for plugging and abandonment costs  
Asset retirement obligation Beginning Balance $ 19,013
Liabilities incurred 640
Liabilities settled (14,800)
Accretion expense 1,599
Revisions in estimated liabilities 3,574
Asset retirement obligation Ending Balance $ 10,026