Share Capital - Changes in Number of Shares of Class A Stock Outstanding (Details) - Common Class A [Member] - shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Class A Stock outstanding, beginning of year	13,139,203	13,261,095
Issued pursuant to shared-based compensation plans	38,728	328,458
Repurchased and canceled pursuant to the stock buy-back	(236,122)	(450,350)
Class A Stock outstanding, end of year	12,941,809	13,139,203

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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-Name Accounting Standards Codification
-Topic 505
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-Section 50
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Reference 2: 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

No definition available.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

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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
-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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