Financial instruments - Effects on Statement of Operations of Derivative Financial Instruments Not Designated as Hedges (Detail) - CAD CAD in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Fair Value of Financial Instruments [Line Items]
Total change in unrealized loss (gain) on derivative financial instruments	CAD (1,990)	CAD 3,046
Total realized loss (gain) on derivative financial instruments	1,918	0
Ineffective portion of derivative financial instruments accounted for as hedges	36	32
Loss (gain) on derivative financial instruments	2,188	(1,375)
Gain (loss) on derivative instruments	(270)	1,375
Not Designated as Hedging Instrument
Fair Value of Financial Instruments [Line Items]
Total change in unrealized loss (gain) on derivative financial instruments	1,421	1,589
Total realized loss (gain) on derivative financial instruments	919	(1,665)
Loss (gain) on derivative financial instruments not accounted for as hedges	2,340	(76)
Not Designated as Hedging Instrument \| Interest rate swaps
Fair Value of Financial Instruments [Line Items]
Total change in unrealized loss (gain) on derivative financial instruments	(1,383)	(1,797)
Total realized loss (gain) on derivative financial instruments	1,498	1,962
Not Designated as Hedging Instrument \| Energy derivative contracts
Fair Value of Financial Instruments [Line Items]
Total change in unrealized loss (gain) on derivative financial instruments	886	3,386
Total realized loss (gain) on derivative financial instruments	(579)	(3,627)
Not Designated as Hedging Instrument \| Foreign exchange forward
Fair Value of Financial Instruments [Line Items]
Total change in unrealized loss (gain) on derivative financial instruments	1,918	0
Designated as Hedging Instrument
Fair Value of Financial Instruments [Line Items]
Ineffective portion of derivative financial instruments accounted for as hedges	CAD (2,610)	CAD 1,451

Fair Value of Financial Instruments [Line Items]

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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Gain (loss) incurred in hedging activities.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

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