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Asset Retirement Obligations - Schedule of Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]    
Balance, beginning of year $ 939 $ 913
Accretion 6 25
Sold/Plugged (18)
New drilled wells 19
Change in discount rate (15)
Liabilities incurred
Balance, end of year $ 930 $ 939