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Inventory, net (Details 1)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
lb
Dec. 31, 2016
USD ($)
lb
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Disclosure of inventory net [Line Items]        
Mineral deposits inventory gross $ 19,435 $ 18,244    
Impairment of mineral deposits (1,467) (123) $ 20,472 $ 7,735
Mineral deposits invenory, net 17,968 18,121    
Mineral deposits inventory, current 14,730 5,586    
Mineral deposits inventory, noncurrent $ 3,238 $ 12,535    
Inventory units in dry metric tonne | lb 1,329,469 1,184,585    
Mineral in stock piles [Member]        
Disclosure of inventory net [Line Items]        
Mineral deposits inventory gross $ 7,173 $ 16,793    
Inventory units in dry metric tonne | lb 463,746 1,085,696    
Fresh mineral in plant [Member]        
Disclosure of inventory net [Line Items]        
Mineral deposits inventory gross $ 11,983 $ 1,248    
Inventory units in dry metric tonne | lb 835,613 74,260    
Tail Mineral [Member]        
Disclosure of inventory net [Line Items]        
Mineral deposits inventory gross $ 279 $ 203    
Inventory units in dry metric tonne | lb 30,110 24,629