The number of shares of common stock and treasury stock and the share activity during the years ended December 31, 2013 and 2012 are as follows:
| Common Shares (thousands) |
Treasury Shares (thousands) |
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| 2013 | 2012 | 2013 | 2012 | |||||||||||||
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Balance at the beginning of the year |
160,120 | 155,939 | 74,757 | 78,938 | ||||||||||||
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Preferred stock conversion to common stock |
— | 875 | — | (875 | ) | |||||||||||
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Stock plan shares issued |
3,589 | 3,538 | (3,589 | ) | (3,538 | ) | ||||||||||
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Shares surrendered by optionees |
(74 | ) | (232 | ) | 74 | 232 | ||||||||||
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Balance at the end of the year |
163,635 | 160,120 | 71,242 | 74,757 | ||||||||||||
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