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Stock-Based Compensation Plans (Tables)
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3 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Mar. 31, 2013
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| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Summary of restricted stock activity | The following is a summary of restricted stock activity for the three months ended March 31, 2013:
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| Schedule of Nonvested Performance-based Units Activity [Table Text Block] | The following is a summary of performance-based share grants for the three months ended March 31, 2013:
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| Summary of the changes in outstanding stock options | The following is a summary of the changes in outstanding stock options for the three months ended March 31, 2013:
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| Weighted-average assumptions for annual March 2012 grants | The fair value of each option grant was estimated on the date of grant using the binomial lattice pricing model which incorporates multiple and variable assumptions over time, including assumptions such as employee exercise patterns, stock price volatility and changes in dividends. The following are weighted-average assumptions for our annual March grants in 2013.
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