Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations (Details)

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Asset Retirement Obligations (Details) (USD $)
In Thousands, unless otherwise specified
9 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Oct. 17, 2013
Medusa Fields, Medusa Spar LLC, And Gulf Of Mexico Shelf Properties [Member]
Subsequent Event [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligations, Beginning of period $ 13,301    
Accretion expense 1,556    
Liabilities incurred 624    
Liabilities settled (497)    
Revisions to estimate (3,477)    
Asset retirement obligations, End of period 11,507    
Less: current asset retirement obligations 6,002 2,336  
Long-term asset retirement obligations at September 30, 2013 5,505 10,965  
Restricted Investments      
Restricted investments 3,800 3,798  
Subsequent Event [Line Items]      
Liabilities settled due to sale of business     $ 4,500