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Mineral Properties, Utah (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Property, Plant and Equipment [Line Items]    
Gain on disposal of mineral property, net $ 358 $ 150
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