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PLANT AND EQUIPMENT AND MINERAL PROPERTIES - Schedule of Summary of Mineral Properties (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property, Plant and Equipment [Line Items]      
Abandonment of mineral properties $ 287 $ 1,036 $ 2,770
Mineral properties 83,539 92,625  
Uranerz ISR properties (a)      
Property, Plant and Equipment [Line Items]      
Mineral properties 25,974 35,060  
Sheep Mountain      
Property, Plant and Equipment [Line Items]      
Mineral properties 34,183 34,183  
Roca Honda      
Property, Plant and Equipment [Line Items]      
Mineral properties 22,095 22,095  
Other      
Property, Plant and Equipment [Line Items]      
Mineral properties $ 1,287 $ 1,287