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Asset Retirement Obligations (Schedule Of Change In Asset Retirement Obligation) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Asset Retirement Obligations [Abstract]          
Asset retirement obligations, Beginning balance     $ 65,701    
Asset retirement obligations, Assumed in acquisition     4,738    
Asset retirement obligations, Divested     (23)    
Asset retirement obligations, Revisions to previous estimates     2,928    
Asset retirement obligations, Liabilities incurred     1,208    
Asset retirement obligations, Liabilities settled     (2,845)    
Asset retirement obligations, Accretion expense 915 719 2,645 2,033  
Asset retirement obligations, Ending balance 74,352   74,352    
Less: Current portion of asset retirement obligations (845)   (845)   (348)
Asset retirement obligations - non-current $ 73,507   $ 73,507   $ 65,353