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Earnings Per Share (Tables) | 3 Months Ended
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Mar. 31, 2013
Earnings Per Share [Abstract] |
Summary of Earnings per share |
|  | Three Months Ended March 31 |
|  | 2013 |  |  | 2012 |
Numerator (in millions): |  |  |  |  |  |  |  |
Net income available to common stockholders |  | $ | 18.0 |  |  | $ | 24.6 |
Denominator (in thousands): |  |  |  |  |  |  |  |
Weighted average common shares outstanding |  |  | 23,404 |  |  |  | 23,055 |
Dilutive effect of stock options and awards |  |  | 611 |  |  |  | 768 |
Denominator for diluted earnings per share |  |  | 24,015 |  |  |  | 23,823 |
Net income per share, basic: |  | $ | 0.77 |  |  | $ | 1.07 |
Net income per share, diluted: |  | $ | 0.75 |  |  | $ | 1.03 |

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations. + References No definition available. + Details
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