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Asset Retirement Obligations - Summary of Asset Retirement Obligation (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]      
Balance, beginning of period $ 4,196us-gaap_AssetRetirementObligation $ 3,834us-gaap_AssetRetirementObligation $ 3,834us-gaap_AssetRetirementObligation
Changes in cash flow estimates      136us-gaap_AssetRetirementObligationRevisionOfEstimate
Costs incurred (48)us-gaap_AssetRetirementObligationLiabilitiesIncurred   (199)us-gaap_AssetRetirementObligationLiabilitiesIncurred
Accretion expense 112us-gaap_AssetRetirementObligationAccretionExpense 79us-gaap_AssetRetirementObligationAccretionExpense 425us-gaap_AssetRetirementObligationAccretionExpense
Balance, end of period 4,260us-gaap_AssetRetirementObligation   4,196us-gaap_AssetRetirementObligation
Less: Current portion (197)us-gaap_AssetRetirementObligationCurrent   (196)us-gaap_AssetRetirementObligationCurrent
Non-current Portion $ 4,063us-gaap_AssetRetirementObligationsNoncurrent   $ 4,000us-gaap_AssetRetirementObligationsNoncurrent