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Mineral Properties (Utah) (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Mar. 31, 2016
Sep. 30, 2016
Sep. 30, 2015
Property, Plant and Equipment [Line Items]      
Gain on disposal of mineral property, net   $ 150 $ 1,958
Utah Sale [Member] | Sold      
Property, Plant and Equipment [Line Items]      
Proceeds from sale of gold project $ 150    
Net smelter return royalty (as a percent) 2.00%    
Gain on disposal of mineral property, net $ 150