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Revenue - Unpriced contract modifications (Details) - CAD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Disaggregation of Revenue [Line Items] |  |
Revenue | $ 410,061 | $ 292,557
Uncollected consideration | 7,526 | 8,020
Variable consideration - unpriced contract modifications |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 250 | 1,168
Accounts receivable |  |
Disaggregation of Revenue [Line Items] |  |
Uncollected consideration | 0 | 358
Contract assets |  |
Disaggregation of Revenue [Line Items] |  |
Uncollected consideration | $ 7,526 | $ 7,662

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