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Stock-based compensation - Options by exercise price range (Details) | 12 Months Ended |  |
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Dec. 31, 2020 $ / shares | Dec. 31, 2020 CAD ($) shares | Dec. 31, 2019 CAD ($) shares | Dec. 31, 2020 CAD ($) $ / shares shares | Dec. 31, 2019 $ / shares | Dec. 31, 2019 CAD ($) $ / shares shares
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] |  |  |  |  |  |
Options outstanding, Number (in shares) | shares |  |  |  | 125,000 |  |
Options outstanding, Weighted average remaining life |  | 1 year 10 months 24 days |  |  |  |
Options outstanding, Weighted average exercise price (in CAD per share) |  |  |  | $ 4.16 |  |
Compensation costs related to non-vested awards not yet recognized | $ |  |  |  | $ 0 |  | $ 0
Stock options granted | shares |  | 0 | 0 |  |  |
$2.75 |  |  |  |  |  |
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] |  |  |  |  |  |
Exercise price (CAD per share) | $ 2.75 |  |  |  |  |
Options outstanding, Number (in shares) | shares |  |  |  | 73,400 |  |
Options outstanding, Weighted average remaining life |  | 1 year 8 months 12 days |  |  |  |
Options outstanding, Weighted average exercise price (in CAD per share) | 2.75 |  |  |  |  |
$5.91 |  |  |  |  |  |
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] |  |  |  |  |  |
Exercise price (CAD per share) | 5.91 |  |  |  |  |
Options outstanding, Number (in shares) | shares |  |  |  | 31,100 |  |
Options outstanding, Weighted average remaining life |  | 3 years |  |  |  |
Options outstanding, Weighted average exercise price (in CAD per share) | 5.91 |  |  |  |  |
$6.56 |  |  |  |  |  |
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] |  |  |  |  |  |
Exercise price (CAD per share) | 6.56 |  |  |  |  |
Options outstanding, Number (in shares) | shares |  |  |  | 20,500 |  |
Options outstanding, Weighted average remaining life |  | 10 months 24 days |  |  |  |
Options outstanding, Weighted average exercise price (in CAD per share) | $ 6.56 |  |  |  |  |
Share option plan |  |  |  |  |  |
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] |  |  |  |  |  |
Options outstanding, Weighted average remaining life |  |  | 2 years 4 months 24 days |  |  |
Options outstanding, Weighted average exercise price (in CAD per share) |  |  |  |  |  | $ 4.61
Options exercisable, Weighted average exercise price (in CAD per share) | (per share) |  |  |  | $ 4.16 | $ 4.61 |
Fair value of options vested | $ |  | $ 0 | $ 0 |  |  |
Total options exercisable (in shares) | shares |  |  |  | 125,000 |  | 238,600

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- Definition Amount of cost not yet recognized for nonvested award under share-based payment arrangement. + 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 (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur. + 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 (e)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. + 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)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term of outstanding stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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