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Utility Plant and Intangible Assets (Details 3) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Reconciliation of the beginning and ending aggregate carrying amount of the asset retirement obligations    
Obligation at the beginning of the period $ 3,095us-gaap_AssetRetirementObligation $ 3,018us-gaap_AssetRetirementObligation
Additional liabilities incurred 6us-gaap_AssetRetirementObligationLiabilitiesIncurred 11us-gaap_AssetRetirementObligationLiabilitiesIncurred
Liabilities settled (66)us-gaap_AssetRetirementObligationLiabilitiesSettled (126)us-gaap_AssetRetirementObligationLiabilitiesSettled
Accretion 199us-gaap_AssetRetirementObligationAccretionExpense 192us-gaap_AssetRetirementObligationAccretionExpense
Obligation at the end of the period $ 3,234us-gaap_AssetRetirementObligation $ 3,095us-gaap_AssetRetirementObligation