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Asset Retirement Obligations - Reconciliation of Beginning and Ending Aggregate Carrying Amounts of Asset Retirement Obligations (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligations at January 1 $ 498,410 $ 128,116 $ 119,877
Liability incurred upon acquiring and drilling wells 5,078 7,479 5,716
Liability assumed in acquisition(1) 0 [1] 371,365 [1] 0 [1]
Revisions in estimated cash flows (3,077) 34,654 7,574
Liability settled or disposed in current period(2) (113,071) [2] (72,200) [2] (14,419) [2]
Accretion(3) 36,777 [3] 28,996 [3] 9,368 [3]
Asset retirement obligations at December 31 424,117 498,410 128,116
Less: current portion 87,063 118,504 32,906
Asset retirement obligations, net of current $ 337,054 $ 379,906 $ 95,210
[1] Represents asset retirement obligations assumed in the acquisitions of oil and natural gas properties in the Gulf of Mexico during the second quarter of 2012.
[2] Year ended December 31, 2013 includes $45.3 million for the decommissioning of various platforms, pipeline and associated wells in the Gulf of Mexico and $15.2 million of asset retirement obligations disposed in conjunction with the sale of the Permian Properties. Years ended December 31, 2013 and 2012 include the settlement of plugging and abandonment obligations associated with properties in the Gulf of Mexico. Year ended December 31, 2011 includes amounts related to the Permian Basin and east Texas properties sold during 2011.
[3] Years ended December 31, 2013 and 2012 include accretion attributable to asset retirement obligations assumed in the acquisitions of oil and natural gas properties in the Gulf of Mexico during the second quarter of 2012.