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Stock-based compensation - Performance and deferred stock unit plan (Details) | 12 Months Ended
--- | ---
Dec. 31, 2019 CAD ($) $ / shares shares | Dec. 31, 2018 CAD ($) $ / shares shares
Performance restricted share units (PSUs) |  |
Number of units |  |
Beginning balance (in shares) | 741,117 | 896,633
Granted (in shares) | 122,274 | 197,763
Vested/redeemed (in shares) | (372,924) |
Forfeited (in shares) | (8,560) |
Ending balance (in shares) | 481,907 | 741,117
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Intrinsic Value, Amount Per Share [Abstract] |  |
Outstanding, beginning of period (CAD per unit) | $ / shares | $ 5.92 | $ 4.81
Granted, Weighted average exercise price (CAD per unit) | $ / shares | 13.12 | 8.01
Vested/redeemed, Weighted average exercise price (CAD per unit) | $ / shares | 4.45 | 4.27
Forfeited, Weighted average exercise price (CAD per unit) | $ / shares | 8.09 |
Outstanding, end of period (CAD per unit) | $ / shares | $ 8.85 | $ 5.92
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |
Risk-free interest rate | 1.43% | 1.98%
Expected volatility | 40.12% | 45.04%
Performance restricted share unit plan | Performance restricted share units (PSUs) |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Award vesting period | 3 years |
Equity classified restricted share unit plan | Performance restricted share units (PSUs) |  |
Number of units |  |
Vested/redeemed (in shares) | (372,924) | (353,279)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Intrinsic Value, Amount Per Share [Abstract] |  |
Total unrecognized compensation costs related to non-vested non-option share-based payment arrangements | $ | $ 2,905,000 | $ 2,713,000
Period for award recognition | 1 year 2 months 12 days | 1 year 3 months 18 days
Settled (in shares) | 334,244 |
Settlement ratio, per PSU (in shares) | 2.00 | 2.00
Deferred share unit plan | Deferred stock units (DSUs) |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |
Annual fixed remuneration | 50.00% |
Percentage of annual bonus eligible for deferred stock units | 50.00% |
Liability classified deferred stock unit plan | Deferred stock units (DSUs) |  |
Number of units |  |
Beginning balance (in shares) | 1,126,239 | 991,583
Granted (in shares) | 82,191 | 134,656
Vested/redeemed (in shares) | (307,385) | 0
Ending balance (in shares) | 901,045 | 1,126,239
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Intrinsic Value, Amount Per Share [Abstract] |  |
Total unrecognized compensation costs related to non-vested non-option share-based payment arrangements | $ | $ 0 |
Settled (in shares) | 307,385 |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |
Fair market value (CAD per share) | $ / shares | $ 15.95 | $ 11.91
Award units settled during the period | $ | $ 5,084,000 | $ 0
Liability classified deferred stock unit plan | Deferred stock units (DSUs) | Accrued liabilities |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |
Current portion of award obligation | $ | 0 | 0
Liability classified deferred stock unit plan | Deferred stock units (DSUs) | Other liabilities |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |  |
Non-current portion of award obligation | $ | $ 14,375,000 | $ 13,413,000

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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://fasb.org/us-gaap/role/ref/legacyRef -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=116856206&loc=d3e5070-113901 + Details
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