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Stock-Based Compensation (Tables)
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3 Months Ended |
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Mar. 31, 2015
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| Summary of Activity Under Stock Option Plans |
A summary of the activity under our stock option plans as of March 31, 2015 and changes during the three month period then ended, is presented below:
| | | | | | | | | | | | | | | Options Outstanding | | Weighted- Average Exercise Price Per Share | | Weighted-Average Remaining Contractual Life in Years | | Aggregate Intrinsic Value | Options outstanding at December 31, 2014 | 393,347 |
| | $ | 40.72 |
| | 3.8 | | $ | 16,019,130 |
| Options granted | — |
| | — |
| | | | |
| Options exercised | (141,097 | ) | | 39.93 |
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| Options forfeited | (850 | ) | | 43.00 |
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| Options outstanding at March 31, 2015 | 251,400 |
| | 41.06 |
| | 3.7 | | 10,344,139 |
| Options exercisable at March 31, 2015 | 237,412 |
| | 40.42 |
| | 3.3 | | 9,920,540 |
| Options vested or expected to vest at March 31, 2015* | 250,980 |
| | 41.05 |
| | 3.7 | | 10,331,431 |
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* In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future. Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options. |
| Assumptions Used in Calculation of Fair Value |
Below are the assumptions used in the Monte Carlo calculation: | | | | | | March 31, 2015 | | March 31, 2014 | Expected volatility | 28.2% | | 33.7% | Expected term (in years) | 3.0 | | 3.0 | Risk-free interest rate | 0.96% | | 0.67% | Expected dividend yield | — | | — |
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| Performance-Based Restricted Stock [Member] |
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| Restricted Stock Activities |
| | | | | Performance-Based Restricted Stock Awards | Non-vested awards outstanding at December 31, 2014 | 92,437 |
| Awards granted | 50,798 |
| Stock issued | (20,910 | ) | Awards forfeited | (6,110 | ) | Non-vested awards outstanding at March 31, 2015 | 116,215 |
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| Time Based Restricted Stock [Member] |
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| Restricted Stock Activities |
| | | | | Time-Based Restricted Stock Awards | Non-vested awards outstanding at December 31, 2014 | 238,386 |
| Awards granted | 62,135 |
| Stock issued | (65,684 | ) | Awards forfeited | (2,960 | ) | Non-vested awards outstanding at March 31, 2015 | 231,877 |
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| Deferred Stock Units [Member] |
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| Restricted Stock Activities |
| | | | | Deferred Stock Units | Awards outstanding at December 31, 2014 | 30,150 |
| Awards granted | — |
| Stock issued | — |
| Awards outstanding at March 31, 2015 | 30,150 |
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