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Shareholders' equity (Tables) | 3 Months Ended
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Mar. 31, 2016
Stockholders' Equity Note [Abstract] |
Common and Preferred Stock Activity | The Common and Preferred Stock Activity table below contains additional information about preferred stock conversions during the three months ended March 31, 2016 and 2015.
Common and Preferred Stock Activity: | Preferred stock |  | Common stock
(in shares) | Series A convertible |  | Treasury | Outstanding
Beginning balance as of December 31, 2015 | 76,539 |  |  | 7,186,521 |  | 87,038,050 |
Repurchase of common stock | — |  |  | — |  | — |
Conversion of convertible preferred stock | (93 | ) |  | — |  | 9,305 |
Issuance for share-based compensation plans | — |  |  | — |  | 12,378 |
Ending balance as of March 31, 2016 | 76,446 |  |  | 7,186,521 |  | 87,059,733 |
Beginning balance as of December 31, 2014 | 78,141 |  |  | 4,786,521 |  | 89,064,582 |
Repurchase of common stock | — |  |  | 1,200,000 |  | (1,200,000 | )
Conversion of convertible preferred stock | (80 | ) |  | — |  | 7,947 |
Issuance for share-based compensation plans | — |  |  | — |  | 10,828 |
Ending balance as of March 31, 2015 | 78,061 |  |  | 5,986,521 |  | 87,883,357 |

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