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Shares - Share purchase program (Details) - CAD ($) $ in Thousands | 2 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Feb. 17, 2021 | Dec. 31, 2020 | Mar. 12, 2020
Equity, Class of Treasury Stock [Line Items] |  |  |
Shares purchased and subsequently cancelled during period (in shares) |  | 1,223,097 |
Share Repurchase Program |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Maximum number of shares to be purchased (in shares) |  |  | 2,300,000,000
Common shares |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Shares purchased and subsequently cancelled during period (in shares) |  | 1,223,097 |
Common shares | Share Repurchase Program |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Shares purchased and subsequently cancelled during period (in shares) |  | 1,223,097,000 |
Increase (decrease) as a result of the retirement of shares |  | $ (9,863) |
Common shares | Share Repurchase Program | Subsequent event |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Shares purchased and subsequently cancelled during period (in shares) | 377,500,000 |  |
Increase (decrease) as a result of the retirement of shares | $ (3,068) |  |
Additional paid-in capital | Subsequent event |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Increase (decrease) as a result of the retirement of shares | $ 1,838 |  |
Additional paid-in capital | Share Repurchase Program |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |
Increase (decrease) as a result of the retirement of shares |  | $ 755 |

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