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Stock-based compensation - Options by exercise price range (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 $ / shares $ / shares shares	Dec. 31, 2019 CAD ($) $ / shares shares	Dec. 31, 2018 CAD ($) $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options outstanding, Number (in shares) | shares	238,600	238,600		238,600
Options outstanding, Weighted average remaining life		2 years 4 months 24 days
Options outstanding, Weighted average exercise price (in CAD per share)	$ 4.61	$ 4.61
$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	85,100	85,100		85,100
Options outstanding, Weighted average remaining life		2 years 8 months 12 days
Options outstanding, Weighted average exercise price (in CAD per share)				$ 2.75
$2.79
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price (CAD per share)	$ 2.79
Options outstanding, Number (in shares) | shares	50,000	50,000		50,000
Options outstanding, Weighted average remaining life		2 years 6 months
Options outstanding, Weighted average exercise price (in CAD per share)				$ 2.79
$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	46,300	46,300		46,300
Options outstanding, Weighted average remaining life		3 years 4 months 24 days
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	34,000	34,000		34,000
Options outstanding, Weighted average remaining life		1 year 7 months 6 days
Options outstanding, Weighted average exercise price (in CAD per share)				$ 6.56
$9.33
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price (CAD per share)	$ 9.33
Options outstanding, Number (in shares) | shares	5,300	5,300		5,300
Options outstanding, Weighted average remaining life		6 months
Options outstanding, Weighted average exercise price (in CAD per share)				$ 9.33
$10.13
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price (CAD per share)	$ 10.13
Options outstanding, Number (in shares) | shares	17,900	17,900		17,900
Options outstanding, Weighted average remaining life		9 months 18 days
Options outstanding, Weighted average exercise price (in CAD per share)				$ 10.13
Share option plan
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options outstanding, Weighted average remaining life			3 years 3 months 18 days
Options outstanding, Weighted average exercise price (in CAD per share)			$ 5.40
Fair value of options vested | $		$ 0	$ 98
Total options exercisable (in shares) | shares	238,600	238,600	565,600	238,600	565,600
Options exercisable, Weighted average exercise price (in CAD per share) | (per share)	$ 4.61	$ 4.61			$ 5.40

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Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price

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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.

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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.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

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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.

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