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Financial instruments (Tables)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Statement [Line Items]    
Disclosure of fair value measurement [Table Text Block]
      Dec. 31, 2017     Dec. 31, 2016  
  Recurring measurements   FV     CV     FV     CV  
  Loans and receivables                        
         Cash and cash equivalents 1 $ 356,499   $ 356,499   $ 146,864   $ 146,864  
         Restricted cash 1   206     206     17,148     17,148  
         Trade and other receivables 1, 2   142,199     142,199     116,445     116,445  
  Fair value through profit or loss                        
         Trade and other receivables - embedded derivatives 3   17,427     17,427     12,538     12,538  
         Non-hedge derivative assets 3   2,841     2,841     3,397     3,397  
         Prepayment option - embedded derivative 7   3,980     3,980     4,430     4,430  
         Investments at FVTPL 4   282     282     192     192  
  Available-for-sale investments 4   21,973     21,973     13,508     13,508  
  Total financial assets   545,407     545,407     314,522     314,522  
  Financial liabilities at amortized cost                        
         Trade and other payables 1, 2   192,448     192,448     163,027     163,027  
         Finance leases   84,573     84,573     12,932     12,932  
         Other financial liabilities 5   19,625     22,568     17,231     22,998  
         Senior unsecured notes 6   1,082,740     991,883     1,040,178     991,004  
         Equipment finance facility 8   -     -     50,267     50,267  
         Senior secured revolving credit facilities 8   -     -     202,075     202,075  
         Unamortized transaction costs 8   (8,328 )   (8,328 )   (6,752 )   (6,752 )
  Fair value through profit or loss                        
         Embedded derivatives 3   1,533     1,533     86     86  
         Warrant liabilities 3   6,961     6,961     7,588     7,588  
         Option liabilities 3   732     732     570     570  
         Non-hedge derivative liabilities 1,3   16,140     16,140     10,682     10,682  
  Total financial liabilities   1,396,424     1,308,510     1,497,884     1,454,477  
  Net financial liability $ (851,017 ) $ (763,103 ) $ (1,183,362 ) $ (1,139,955 )
 
Disclosure of significant unobservable inputs used in fair value measurement of assets and liabilities [Table Text Block]
  December 31, 2017   Level 1     Level 2     Level 3     Total  
  Financial assets measured at fair value                        
  Financial assets at FVTPL:                        
       Embedded derivatives $   -   $ 17,427   $ -   $ 17,427  
       Non-hedge derivatives   -     2,841     -     2,841  
       Investments at FVTPL   -     282     -     282  
  Prepayment option embedded derivative   -     3,980     -     3,980  
  Available-for-sale investments   21,973     -     -     21,973  
                           
    $ 21,973   $ 24,530   $   -   $ 46,503  
  Financial liabilities measured at fair value                        
  Financial liabilities at FVTPL:                        
       Embedded derivatives $   -   $ 1,533   $ -   $ 1,533  
       Non-hedge derivatives   -     16,140     -     16,140  
       Option liability   -     732     -     732  
       Warrant liabilities   6,961     -     -     6,961  
                           
    $ 6,961   $ 18,405   $ -   $ 25,366  
  December 31, 2016   Level 1     Level 2     Level 3     Total  
  Financial assets measured at fair value                        
  Financial assets at FVTPL:                        
       Embedded derivatives $   -   $ 12,538   $   -   $ 12,538  
       Non-hedge derivatives   -     3,397     -     3,397  
       Investments at FVTPL   -     192     -     192  
  Prepayment option embedded derivative   -     4,430     -     4,430  
  Available-for-sale investments   12,018     -     1,490     13,508  
                           
    $ 12,018   $ 20,557   $ 1,490   $ 34,065  
  Financial liabilities measured at fair value                        
  Financial liabilities at FVTPL:                        
       Embedded derivatives $   -   $ 86   $   -   $ 86  
       Non-hedge derivatives   -     10,682     -     10,682  
  Option liability   -     570     -     570  
       Warrant liabilities   7,588     -     -     7,588  
                           
    $ 7,588   $ 11,338   $   -   $ 18,926  
Disclosure of detailed information about foreign currency risk [Table Text Block]
            Dec. 31, 2017     Dec. 31, 2016              
    $   CAD 1     USD 2     PEN 3     CAD 1     USD 2     PEN 3  
  Cash and cash equivalents   9,518   $ 20,597   $ 3,692 $     4,759 $     8,121   $ 3,440  
  Trade and other receivables   530     77,824     1,114     720     28,639     2,503  
  Other financial assets   22,255     -     -     13,279     -     -  
  Trade and other payables   (6,115 )   (9,687 )   (17,917 )   (20,014 )   (4,303 )   (17,145 )
  Other financial liabilities   (6,961 )   -     (22,568 )   (7,588 )   -     (22,998 )
    $   19,227   $ 88,734   $ (35,679 ) $   (8,844 ) $   32,457   $ (34,200 )
 
Disclosure of foreign currency risk [Table Text Block]
            Would have changed     Would have changed  
  December 31, 2017   Change of:     2017 after-tax profit by:     2017 after-tax OCI by:  
  USD/CAD exchange rate 1   + 10%   $ 5.6 million   $ (2.0) million  
  USD/CAD exchange rate 1   - 10%     (6.8) million     2.4 million  
  USD/PEN exchange rate 2   + 10%     2.1 million     - million  
  USD/PEN exchange rate 2   - 10%     (2.6) million     - million  
            Would have changed     Would have changed  
  December 31, 2016   Change of:     2016 after-tax profit by:     2016 after-tax OCI by:  
  USD/CAD exchange rate 1   + 10%     3.9 million     (1.2) million  
  USD/CAD exchange rate 1   - 10%     (4.9) million     1.5 million  
  USD/PEN exchange rate 2   + 10%     2.0 million     - million  
  USD/PEN exchange rate 2   - 10%     (2.5) million     - million  
Disclosure of commodity price risk [Table Text Block]
            Would have changed     Would have changed  
  December 31, 2017   Change of:     2017 after-tax profit by:     2017 after-tax OCI by:  
  Copper prices ($/lb) 3   + $0.30   $ (2.3) million   $   - million  
  Copper prices ($/lb) 3   - $0.30     2.3 million     - million  
  Zinc prices ($/lb) 4   + $0.10     0.9 million     - million  
  Zinc prices ($/lb) 4   - $0.10     (0.9) million     - million  
            Would have changed     Would have changed  
  December 31, 2016   Change of:     2016 after-tax profit by:     2016 after-tax OCI by:  
  Copper prices ($/lb) 3   + $0.30   $ (4.8 ) million $   - million  
  Copper prices ($/lb) 3   - $0.30     4.7 million     - million  
  Zinc prices ($/lb) 4   + $0.10     0.3 million     - million  
  Zinc prices ($/lb) 4   - $0.10     (0.3 ) million   - million  
Disclosure of share price risk explanatory [Table Text Block]
            Would have changed     Would have changed  
  December 31, 2017   Change of:     2017 after-tax profit by:     2017 after-tax OCI by:  
  Share prices 5   + 25%   $   - million   $ 5.5 million  
  Share prices 5   - 25%     (1.9) million     (3.6) million  
            Would have changed     Would have changed  
  December 31, 2016   Change of:     2016 after-tax profit by:     2016 after-tax OCI by:  
  Share prices 5   + 25%   $   - million   $ 4.5 million  
  Share prices 5   - 25%     (0.8) million     (3.7) million  
Disclosure of interest rate risk [Table Text Block]
            Would have changed     Would have changed  
  December 31, 2017   Change of:     2017 after-tax profit by:     2017 after-tax OCI by:  
  Interest rates   + 2.00%   $ 0.4 million   $   - million  
  Interest rates   - 2.00%     (2.8) million     - million  
            Would have changed     Would have changed  
  December 31, 2016   Change of:     2016 after-tax profit by:     2016 after-tax OCI by:  
  Interest rates   + 2.00%   $ (5.0) million   $   - million  
  Interest rates   - 2.00%     0.7 million     - million  
Disclosure of liquidity risk [Table Text Block]
      Carrying     Contractual     12 months                 More than  
  Dec. 31, 2017   amount     cash flows     or less     13 - 36 months     37 - 60 months       60 months  
  Assets used to manage liquidity risk                                
  Cash and cash equivalents $ 356,499   $ 356,499   $ 356,499   $   -   $   -   $   -  
  Trade and other receivables   142,199     147,196     124,134     12,403     10,659     -  
  Non-hedge derivative asset   2,841     2,841     2,841     -     -     -  
    $ 501,539   $ 506,536   $ 483,474   $ 12,403   $ 10,659   $   -  
  Non-derivative financial liabilities                                
  Trade and other payables, including embedded derivative $ (192,821 ) $ (192,821 ) $ (192,821 ) $ -   $   -   $   -  
  Other financial liabilities   (22,568 )   (37,216 )   (3,824 )   (4,791 )   (4,780 )   (23,821 )
  Long-term debt, including prepayment option embedded derivative   (979,575 )   (1,520,416 )   (79,715 )   (159,430 )   (152,396 )   (1,128,875 )
  Finance lease liabilities   (84,573 )   (89,750 )   (20,186 )   (40,253 )   (29,311 )   -  
    $ (1,279,537 ) $ (1,840,203 ) $ (296,546 ) $ (204,474 )  $ (186,487 ) $ (1,152,696 )
  Derivative financial liabilities                                
  Warrant liabilities $ (6,961 ) $ (6,961 ) $ (6,961 ) $   -   $ -   $   -  
  Gold option   (732 )   (732 )   (732 )   -     -     -  
  Non-hedge derivative contracts   (16,140 )   (16,140 )   (15,263 )   (877 )   -     -  
    $ (23,833 ) $ (23,833 ) $ (22,956 ) $   (877 ) $   -   $   -  
                                    More  
      Carrying     Contractual     12 months or                 than 60  
  Dec. 31, 2016   amount     cash flows     less     13 - 36 months     37 - 60 months     months  
  Assets used to manage liquidity risk                                
  Cash and cash equivalents $ 146,864   $ 146,864   $ 146,864   $   -   $   -   $   -  
  Trade and other receivables   116,445     116,445     96,221     1,543     18,681     -  
  Non-hedge derivative assets   3,397     3,397     3,397     -     -     -  
    $ 266,706   $ 266,706   $ 246,482   $ 1,543   $ 18,681   $   -  
  Non-derivative financial liabilities                                
  Trade and other payables, including embedded derivatives $ (163,113 ) $ (163,113 ) $ (163,113 ) $ -   $   -   $   -  
  Other financial liabilities   (22,998 )   (35,392 )   (4,025 )   (3,303 )   (4,616 )   (23,448 )
  Long-term debt, including prepayment option embedded derivative   (1,232,164 )   (1,946,925 )   (105,278 )   (105,278 )   (544,957 )   (1,191,412 )
  Finance lease liabilities   (12,932 )   (13,720 )   (3,508 )   (3,338 )   (6,874 )   -  
    $ (1,431,207 ) $ (2,159,150 )  $ (275,924 ) $ (111,919 ) $   (556,447 )  $ (1,214,860 ) 
  Derivative financial liabilities                                
  Warrant liabilities $ (7,588 ) $ (7,588 ) $   -   $   -   $ (7,588 ) $   -  
  Gold option   (570 )   (570 )   -     -     (570 )   -  
  Non-hedge derivative contracts   (10,682 )   (10,682 )   (10,682 )   -     -     -  
    $ (18,840 ) $ (18,840 ) $ (10,682 ) $   -   $ (8,158 )  $ -