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Significant accounting policies - Stock-based compensation (Details) - CAD ($) |  |  | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Equipment expense |  |  | $ 177,532,000 | $ 243,427,000
Impairment of long-lived assets | $ 0 | $ 0 |  |
Number of trading days used to determine weighted average trading price of common shares |  |  | 5 days |
Inventory Error |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Equipment expense |  |  |  | (2,775,000)
Equipment expense net |  |  |  | $ (2,040,000)
Minimum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Ownership percentage | 20.00% |  | 20.00% |
Maximum |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Ownership percentage | 50.00% |  | 50.00% |
Restricted Share Unit (RSU) |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Award service period |  |  | 2 years |
Award vesting period |  |  | 3 years |
Compensation expense recognition period |  |  | 3 years |
Phantom Share Units (PSUs) |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Award vesting period |  |  | 3 years |
Compensation expense recognition period |  |  | 3 years |

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- Definition This element represents equipment expense including depreciation, repairs, rentals, and service contract costs. This item also includes equipment purchases which do not qualify for capitalization in accordance with the entity's accounting policy. This item may also include furniture expenses. + References No definition available. + Details
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