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Financial instruments and risk management - Financial instruments (Details) - CAD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Level 2 | Carrying Amount |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Capital lease obligations | $ 86,568 | $ 66,969
Long-term debt | 39,976 | 40,000
Level 2 | Carrying Amount | Mortgage |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | 19,900 | 0
Level 2 | Fair Value |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Capital lease obligations | 78,373 | 61,872
Long-term debt | 48,371 | 38,700
Level 2 | Fair Value | Mortgage |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | 19,900 | 0
Level 3 | Carrying Amount | Credit facilities |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | 194,918 | 32,000
Level 3 | Fair Value | Credit facilities |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | 194,918 | 32,000
Equipment promissory note | Level 2 | Carrying Amount | Promissory notes |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | 42,937 | 0
Equipment promissory note | Level 2 | Fair Value | Promissory notes |  |
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] |  |
Long-term debt | $ 42,937 | $ 0

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