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Asset Retirement Obligation (Tables)
12 Months Ended
Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]  
Reconciliation of total reclamation liability for asset retirement obligations The following is a reconciliation of the total reclamation liability for asset retirement obligations.
Balance at December 31, 2018$13,322 
Additions and revisions of prior estimates(5,114)
Accretion expenses687 
Settlement of liability(2,753)
Balance at December 31, 2019$6,142 
Additions and revisions of prior estimates8,458 
Accretion expenses396 
Settlement of liability— 
Balance at December 31, 2020$14,996