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
3 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset retirement obligations at beginning of the period $ 6,732  
Accretion expense 228  
Liabilities incurred 272  
Revisions to estimate 18  
Asset retirement obligations at end of period 7,250  
Less: current asset retirement obligations 4,483 4,120
Long-term asset retirement obligations at the end of the period 2,767 2,612
Restricted Investments    
Restricted investments $ 3,806 $ 3,806