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Deferred income tax (Details) - USD ($) $ in Thousands | 12 Months Ended
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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)

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