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Share Capital (Tables) | 12 Months Ended
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Dec. 31, 2017
Equity [Abstract] |
Changes in Number of Shares of Class A Stock Outstanding | The following table reflects changes in the number of shares of Class A Stock outstanding for the periods indicated:
| 2017 |  | 2016
Class A Stock outstanding, beginning of year | 13,261,095 |  |  | 13,238,486 |
Issued pursuant to shared-based compensation plans (note 14) | 328,458 |  |  | 283,471 |
Repurchased and canceled pursuant to the stock buy-back | (450,350 | ) |  | (260,862 | )
Class A Stock outstanding, end of year | 13,139,203 |  |  | 13,261,095 |

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- Definition Tabular disclosure of the change in common stock outstanding. + References No definition available. + Details
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