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Income taxes - Summary of Unrecognized Tax Losses (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Tax effect of tax losses $ 160,052 $ 167,030
Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Tax effect of tax losses 137,268  
Brazil [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Tax effect of tax losses 5,538  
Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Tax effect of tax losses 17,246  
2019 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 14,964  
2019 [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 14,964  
2020 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 25,221  
2020 [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 25,221  
2021 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,451  
2021 [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,451  
2022 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 8,007  
2022 [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 8,007  
2023 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,337  
2023 [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,337  
2025 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 7,894  
2025 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 7,894  
2026 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 14,966  
2026 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 14,966  
2027 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,638  
2027 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 10,638  
2028 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 25,971  
2028 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 25,971  
2029 [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 23,444  
2029 [Member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 23,444  
2030 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 7,282  
2030 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 7,282  
2031 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 45,351  
2031 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 45,351  
2032 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 74,855  
2032 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 74,855  
2033 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 64,883  
2033 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 64,883  
2034 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 58,689  
2034 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 58,689  
2035 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 55,266  
2035 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 55,266  
2036 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 50,503  
2036 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 50,503  
2037 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 27,333  
2037 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 27,333  
2038 [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 9,025  
2038 [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 9,025  
No Expiry [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 32,407  
No Expiry [member] | Brazil [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 32,407  
Tax losses carried forward [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 577,487  
Tax losses carried forward [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 476,100  
Tax losses carried forward [member] | Brazil [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 32,407  
Tax losses carried forward [member] | Greece [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 68,980  
Capital losses with no expiry [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses 64,837  
Capital losses with no expiry [member] | Canada [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Gross amount of the tax losses $ 64,837