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Stock-based compensation Stock-based compensation - Deferred stock unit plan (Details) - Deferred stock units (DSUs) - CAD / shares | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Liability classified deferred stock unit plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |
Beginning balance (units) | 530,622 | 586,834 | 625,156
Granted/issued (units) | 0 | 7,674 | 141,509
Modified (units) | 571,569 |  |
Redeemed (units) | (173,317) | (63,886) | (179,831)
Ending balance (units) | 928,874 | 530,622 | 586,834
Equity classified deferred stock unit plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |  |  |
Beginning balance (units) | 169,728 | 0 |
Granted/issued (units) | 378,867 | 161,007 |
Dividend equivalents granted/issued (units) | 22,974 | 8,721 |
Modified (units) | 571,569 |  |
Ending balance (units) | 0 | 169,728 | 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |  |  |
Outstanding, beginning of period (CAD per unit) | CAD 6.50 | CAD 0.00 |
Granted/Issued, Weighted average exercise price (CAD per unit) | 3.29 | 6.52 |
Dividend equivalents granted/issued, Weighted average exercise price (CAD per unit) | 3.07 | 6.10 |
Modified, Weighted average exercise price (CAD per unit) | 2.58 |  |
Outstanding, end of period (CAD per unit) | CAD 0.00 | CAD 6.50 | CAD 0.00

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Dividend Equivalents Granted + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Dividend Equivalents Granted, Weighted Average Grant Date Fair Value + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Modified in Period + References No definition available. + Details
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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Modified in Period, Weighted Average Grant Date Fair Value + References No definition available. + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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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. + Details
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- Definition The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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