Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations (Details)

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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Jun. 30, 2019
Asset Retirement and Reclamation Obligations    
Estimated Future Cash Undiscounted Amount   $ 29,800
Change in estimated liability $ 2,840