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Stock-based compensation - Stock-based compensation expenses (Details) - General and administrative expenses - CAD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |
Stock-based compensation expenses | $ 1,944 | $ 9,443
Equity classified restricted share unit plan |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |
Stock-based compensation expenses | 1,991 | 1,933
Performance restricted share unit plan |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |
Stock-based compensation expenses | 2,031 | 1,892
Liability classified deferred stock unit plan |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |
Stock-based compensation expenses | $ (2,078) | $ 5,618

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