Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations - Reconciliation of Asset Retirement Obligations Liability (Details)

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Asset Retirement Obligations - Reconciliation of Asset Retirement Obligations Liability (Details) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Jun. 30, 2014
Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligations, beginning of period $ 354,422  
Liabilities settled (30,338)  
Accretion of discount 10,112  
Liabilities assumed through acquisition 15,086 [1]  
Liabilities incurred 755  
Revisions of estimated liabilities 7,566 [2]  
Asset retirement obligations, end of period 357,603  
Less current portion 69,923 77,785
Long-term $ 287,680 $ 276,637
[1] Includes the Woodside Properties acquisition and another immaterial acquisition.
[2] Revisions were primarily due to increased estimates related to work requiring coiled tubing at two locations and removal of a platform at one location.