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Asset Retirement Obligations (Schedule Of Change In Asset Retirement Obligation) (Details) (USD $)
In Thousands, unless otherwise specified
0 Months Ended 12 Months Ended
Dec. 31, 2010
Dec. 31, 2012
Dec. 31, 2011
Asset Retirement Obligations [Abstract]      
Asset retirement obligations, Beginning balance   $ 92,561 $ 69,230
Asset retirement obligations, Assumed in acquisition   14,581  
Asset retirement obligations, Revisions to previous estimates   17,278 [1] 18,609 [1]
Asset retirement obligations, Liabilities incurred   1,185 377
Asset retirement obligations, Liabilities settled   (4,262) (248)
Asset retirement obligations, Accretion expense 130 5,648 4,593
Asset retirement obligations, Ending balance 69,230 126,991 92,561
Less: Current portion of asset retirement obligations   (1,426) (348)
Asset retirement obligations - non-current   $ 125,565 $ 92,213
[1] In 2012, we recorded an upward revision to previous estimates for our asset retirement obligations primarily due to changes in the estimated abandonment dates. In 2011, we recorded upward revisions to previous estimates for our asset retirement obligations due to increases in future plugging and abandonment costs and changes to the remaining lives of our wells