Stock-based compensation - Restricted share unit plan (Details) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020 CAD ($) $ / shares shares	Dec. 31, 2019 CAD ($) $ / shares shares	Dec. 31, 2019 CAD ($) $ / shares shares
Performance restricted share units (PSUs)
Number of units
Beginning balance (in shares)	481,907	741,117	741,117
Granted (in shares)	211,754	122,274	122,274
Vested (in shares)	(201,104)	(372,924)	(372,924)
Forfeited (in shares)		(8,560)	(8,560)
Ending balance (in shares)	492,557	481,907	481,907
Weighted-average exercise price $ per share
Outstanding, beginning of period (CAD per unit) \| $ / shares	$ 8.85	$ 5.92
Granted, Weighted average exercise price (CAD per unit) \| $ / shares	8.55	13.12
Vested, Weighted average exercise price (CAD per unit) \| $ / shares	8.51	4.45
Forfeited, Weighted average exercise price (CAD per unit) \| $ / shares			$ 8.09
Outstanding, end of period (CAD per unit) \| $ / shares	$ 8.86	$ 8.85
Vested (in shares)	201,104	372,924	372,924
Liability classified restricted share unit plan \| Restricted share units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition in years following grant	2 years
Award vesting period	3 years
Equity classified restricted share unit plan \| Restricted share units (RSUs)
Number of units
Beginning balance (in shares)	650,077	948,093	948,093
Granted (in shares)	298,142	193,450	193,450
Vested (in shares)	(269,484)	(465,194)	(465,194)
Forfeited (in shares)	(37,264)	(26,272)	(26,272)
Ending balance (in shares)	641,471	650,077	650,077
Weighted-average exercise price $ per share
Outstanding, beginning of period (CAD per unit) \| $ / shares	$ 9.35	$ 5.88
Granted, Weighted average exercise price (CAD per unit) \| $ / shares	8.55	13.40
Vested, Weighted average exercise price (CAD per unit) \| $ / shares	6.19	4.15
Forfeited, Weighted average exercise price (CAD per unit) \| $ / shares	8.81	6.01
Outstanding, end of period (CAD per unit) \| $ / shares	$ 10.34	$ 9.35
Total unrecognized compensation costs related to non-vested non-option share-based payment arrangements \| $	$ 3,290	$ 3,104	$ 3,104
Period for award recognition	1 year 7 months 6 days	1 year 3 months 18 days	1 year 3 months 18 days
Vested (in shares)	269,484	465,194	465,194
Settled (in shares)		426,514	426,514
Equity classified restricted share unit plan \| Performance restricted share units (PSUs)
Number of units
Vested (in shares)	(201,104)	(372,924)	(372,924)
Weighted-average exercise price $ per share
Total unrecognized compensation costs related to non-vested non-option share-based payment arrangements \| $	$ 3,405	$ 2,905	$ 2,905
Period for award recognition	1 year 7 months 6 days	1 year 2 months 12 days	1 year 2 months 12 days
Vested (in shares)	201,104	372,924	372,924
Settled (in shares)		334,244	334,244

Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Subsequent to Year of Grant

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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).

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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).

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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.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares purchased for issuance under share-based payment arrangement.

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