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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, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Asset Retirement Obligations [Abstract]          
Asset retirement obligations, Beginning balance     $ 126,991    
Asset retirement obligations, Assumed in acquisition     10,676    
Asset retirement obligations, Revisions to previous estimates     3,934    
Asset retirement obligations, Liabilities incurred     229    
Asset retirement obligations, Liabilities settled     (4,659)    
Asset retirement obligations, Accretion expense 1,921 1,412 5,411 4,109  
Asset retirement obligations, Ending balance 142,582   142,582    
Less: Current portion of asset retirement obligations (1,729)   (1,729)   (1,426)
Asset retirement obligations - non-current $ 140,853   $ 140,853   $ 125,565