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Utility Plant and Intangible Assets 3 (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Reconciliation of the beginning and ending aggregate carrying amount of the asset retirement obligations    
Obligation at the beginning of the period $ 4,963 $ 4,393
Additional liabilities incurred 256 562
Liabilities settled (46) (229)
Accretion 55 237
Obligation at the end of the period $ 5,228 $ 4,963