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
Asset Retirement Obligations  
Asset retirement obligations - beginning of period $ 11,859
Obligations incurred 261
Accretion expense 302
Asset retirement obligations - end of period $ 12,422