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Share capital (Tables) | 3 Months Ended
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Mar. 31, 2013
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:
|  | Three months ended March 31, |
|  | 2013 |  |  | 2012 |
Class A Stock outstanding, beginning of period |  |  | 13,508,318 |  |  |  | 13,572,265 |
Issued pursuant to shared-based compensation plans |  |  | — |  |  |  | 16,797 |
Repuchsed and cancelled pursuant to the stock buy-back |  |  | — |  |  |  | (99,900 | )
Class A Stock outstanding, end of period |  |  | 13,508,318 |  |  |  | 13,489,162 |

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