Annual report pursuant to Section 13 and 15(d)

Asset Retirement Obligations (Details)

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Asset Retirement Obligations (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligations at beginning of the period $ 13,301 $ 13,938
Accretion expense 1,785 2,253
Liabilities incurred 679 205
Liabilities settled (457) (1,073)
Liabilities related to oil and gas properties sold (4,765) (877)
Revisions to estimate (3,811) (1,145)
Asset retirement obligations at end of period 6,732 13,301
Less: current asset retirement obligations (4,120) (2,336)
Long-term asset retirement obligations at the end of the period 2,612 10,965
Restricted Investments    
Restricted investments $ 3,806 $ 3,798