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Income taxes - Income (Loss) Before Taxes (Detail) - CAD CAD in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items] |  |
Income/(loss) before taxes | CAD 226,040 | CAD 129,510
Canadian operations |  |
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items] |  |
Income/(loss) before taxes | (3,269) | 29
U.S. operations |  |
Schedule of Components of Income Before Income Tax Expense (Benefit) [Line Items] |  |
Income/(loss) before taxes | CAD 229,309 | CAD 129,481

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- Definition Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(1)(i)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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