Share capital - Changes in Number of Shares of Class A Stock Outstanding (Details) - Class A Stock - shares	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Class A Stock outstanding, beginning of year	12,381,778	12,698,703
Issued pursuant to shared-based compensation plans	242,450	401,597
Repurchased and canceled pursuant to the stock buy-back	(177,192)	(718,522)
Class A Stock outstanding, end of year	12,447,036	12,381,778

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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

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- Definition

Number of shares issued under share-based payment arrangement.

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- Definition

Number of shares of common and preferred stock retired from treasury during the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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