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Financial instruments and risk management - Risk management (Details) - CAD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
COVID-19 |  |
Concentration Risk [Line Items] |  |
Salary and wage subsidies | $ 28,232 |
Reduction in project costs | 16,241 |
Reduction in equipment expense | 9,107 |
Reduction in general and administrative costs | $ 2,884 |
Customer A | Revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 45.00% | 33.00%
Customer B | Revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 30.00% | 22.00%
Customer C | Revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 11.00% | 13.00%
Customer D | Revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 10.00% | 27.00%
Customer 1 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 39.00% | 36.00%
Customer 2 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 20.00% | 12.00%
Customer 3 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 16.00% | 13.00%
Customer 4 | Accounts receivable and contract assets | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 0.00% | 25.00%
Credit Facility |  |
Concentration Risk [Line Items] |  |
Outstanding balance, long-term debt | $ 220,000 | $ 190,000
Basis on variable rate, adjustment | 1.00% |
Corresponding change in annual interest expense | $ 2,200 |

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