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
6 Months Ended
Jun. 30, 2014
Asset Retirement Obligations  
Asset retirement obligations - beginning of period $ 11,859
Obligations incurred 618
Accretion expense 611
Asset retirement obligations - end of period $ 13,088