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Financial instruments and risk management - Risk management (Details) - CAD CAD in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015
Customer A | Total revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 47.00% | 34.00%
Customer B | Total revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 25.00% | 10.00%
Customer C | Total revenues | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 21.00% | 41.00%
Customer 1 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 42.00% | 42.00%
Customer 2 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 22.00% | 5.00%
Customer 3 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 13.00% | 0.00%
Customer 4 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 13.00% | 21.00%
Customer 5 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 7.00% | 20.00%
Customer 6 | Accounts receivable and unbilled revenue | Major customers |  |
Concentration Risk [Line Items] |  |
Concentration risk, percentage | 3.00% | 11.00%
Credit facilities |  |
Concentration Risk [Line Items] |  |
Outstanding balance, long-term debt | CAD 39.6 | CAD 28.6
Basis points | 100.00% |
Corresponding change in annual interest expense | CAD 0.4 |

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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611 + Details
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