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Deferred income tax (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) $ 27,339 $ 13,551  
Deferred tax expense (income) 9,998 (5,825) $ 14,060
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 9,916 (7,963) 1,301
Deferred income tan other income (542)    
Deferred tax liability (asset) 6,883 27,339 13,551
Deferred liability for mining royalties [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (161) (35)  
Deferred tax expense (income) 158 (126)  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (2) (161) (35)
Deferred Liability For Derivative Financial Instruments [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 0 0  
Deferred tax expense (income) 0 0  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss (813) 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (813) 0 0
Deferred asset [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 196,819 179,884  
Deferred tax expense (income) 22,264 8,972  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss (9,103) 7,963  
Deferred income tan other income (542)    
Deferred tax liability (asset) 209,438 196,819 179,884
Deferred asset [Member] | Less - Allowance for deferred asset [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (38,910) (37,012)  
Deferred tax expense (income) (2,038) (1,898)  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred tax liability (asset) (40,948) (38,910) (37,012)
Deferred asset [Member] | Deferred asset for income tax before allowance [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 226,503 215,713  
Deferred tax expense (income) 24,389 10,790  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income (542)    
Deferred tax liability (asset) 250,350 226,503 215,713
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Unused tax losses [member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 94,939 93,050  
Deferred tax expense (income) 11,680 1,889  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income (396)    
Deferred tax liability (asset) 106,223 94,939 93,050
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Difference in depreciation and amortization rates [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 61,617 60,883  
Deferred tax expense (income) 6,497 734  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) 68,114 61,617 60,883
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Provision for closure of mining units, net [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 44,568 39,538  
Deferred tax expense (income) 3,291 5,030  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) 47,859 44,568 39,538
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Other temporary differences [member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 15,459 14,650  
Deferred tax expense (income) 5,369 809  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income (146)    
Deferred tax liability (asset) 20,682 15,459 14,650
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Less - Allowance for deferred asset [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred income tan other income 0    
Deferred asset [Member] | Deferred asset for income tax before allowance [Member] | Impairment loss of long-lived assets [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 9,920 7,592  
Deferred tax expense (income) (2,448) 2,328  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) 7,472 9,920 7,592
Deferred asset [Member] | Deferred asset included in retained earnings [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 196,696 179,841  
Deferred tax expense (income) 22,351 8,892  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss (9,103) 7,963  
Deferred income tan other income (542)    
Deferred tax liability (asset) 209,402 196,696 179,841
Deferred asset [Member] | Deferred asset included in retained earnings [Member] | Derivative financial instruments [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 9,103 1,140  
Deferred tax expense (income) 0 0  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss (9,103) 7,963  
Deferred income tan other income 0    
Deferred tax liability (asset) 0 9,103 1,140
Deferred asset [Member] | Deferred assets for mining royalties [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 123 43  
Deferred tax expense (income) (87) 80  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) 36 123 43
Deferred asset [Member] | Deferred assets for mining royalties [Member] | Other temporary differences [member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 123 43  
Deferred tax expense (income) (87) 80  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred tax liability (asset) 36 123 43
Deferred asset [Member] | Deferred liability for mining royalties [Member] | Other temporary differences [member]      
Disclosure of Deferred income tax [Line Items]      
Deferred income tan other income 0    
Deferred asset [Member] | Deferred asset for income tax after allowance [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) 187,593 178,701  
Deferred tax expense (income) 22,351 8,892  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred tax liability (asset) 209,402 187,593 178,701
Deferred liability [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (169,480) (166,333)  
Deferred tax expense (income) (32,262) (3,147)  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss (813) 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (202,554) (169,480) (166,333)
Deferred liability [Member] | Deferred liability for income tax [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (169,319) (166,298)  
Deferred tax expense (income) (32,420) (3,021)  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (201,739) (169,319) (166,298)
Deferred liability [Member] | Deferred liability for income tax [Member] | Other temporary differences [member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (77,603) (43,985)  
Deferred tax expense (income) 3,123 (33,618)  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (74,480) (77,603) (43,985)
Deferred liability [Member] | Deferred liability for income tax [Member] | Effect of translation into U.S. dollars [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (46,023) (70,525)  
Deferred tax expense (income) (15,248) 24,502  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) (61,271) (46,023) (70,525)
Deferred liability [Member] | Deferred liability for income tax [Member] | Differences in amortization rates for development costs [Member]      
Disclosure of Deferred income tax [Line Items]      
Deferred tax liability (asset) (45,693) (51,788)  
Deferred tax expense (income) (20,295) 6,095  
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss 0 0  
Deferred income tan other income 0    
Deferred tax liability (asset) $ (65,988) $ (45,693) $ (51,788)