Other long-term liabilities and deferred credits - Changes in Environmental Remediation Obligation (Details) - CAD CAD in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Accrual for Environmental Loss Contingencies [Roll Forward]
Opening Balance	CAD 71,529	CAD 70,072
Remediation activities	(1,389)	(10,621)
Accretion	2,464	2,147
Changes in cash flow estimates	2,088	3,171
Revision in assumptions	(9,101)	(5,843)
Foreign exchange rate adjustment	(2,213)	12,603
Closing Balance	CAD 63,378	CAD 71,529

Accrual for Environmental Loss Contingencies, Accretion

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- Definition

Accrual for Environmental Loss Contingencies, Increase (Decrease) for Revision in Assumptions

+ References

No definition available.

+ Details

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- Definition

Accrual for Environmental Loss Contingencies, Remediation Activities

+ References

No definition available.

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- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

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- Definition

Amount of foreign currency translation gain (loss) which decreases (increases) the accrual for environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q2)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Foreign Currency Translation
-URI http://asc.fasb.org/extlink&oid=6513664

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- Definition

Amount of expense (reversal of expense) which increases (decreases) the accrual for environmental loss contingencies from revisions in estimates to existing obligations. Excludes changes related to business acquisitions, divestitures, or currency movement.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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