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Financial instruments and risk management - Risk management (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Customer 1 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 36.00% | 16.00%
Customer 2 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 25.00% | 8.00%
Customer 3 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 13.00% | 33.00%
Customer 4 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 12.00% | 12.00%
Credit facilities |  |
Concentration Risk [Line Items] |  |
Outstanding balance, long-term debt | $ 190.0 | $ 194.9
Basis on variable rate, adjustment | 1.00% |
Corresponding change in annual interest expense | $ 1.9 |

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