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Accounting Policies Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Beginning balance $ 4,064 $ 3,772  
Liabilities acquired 768 0  
Accretion expense 359 292 $ 266
Ending balance $ 5,191 $ 4,064 $ 3,772