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Equity Incentive Plans and Stock-Based Compensation (Tables) | 3 Months Ended
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Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Shares available for grant under stock-based incentive plans | A summary of shares available for grant under the Company’s plans is as follows:
| Shares Available for Grant
Shares available as of December 31, 2013 | 2,527,428 |
Stock options granted | (1,797,462 | )
Stock options forfeited | 269,083 |
Stock options expired under former plans | (9,900 | )
Nonvested equity stock and stock units granted (1) | (308,712 | )
Nonvested equity stock and stock units forfeited (1) | 19,621 |
Total available for grant as of March 31, 2014 | 700,058 |
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(1) | For purposes of determining the number of shares available for grant under the 2006 Plan against the maximum number of shares authorized, each share of restricted stock granted reduces the number of shares available for grant by 1.5 shares and each share of restricted stock forfeited increases shares available for grant by 1.5 shares.
Schedule of stock option activity | The following table summarizes stock option activity under the 1997 Plan and 2006 Plan for the three months ended March 31, 2014 and information regarding stock options outstanding, exercisable, and vested and expected to vest as of March 31, 2014.
| Options Outstanding |  |  |  |
| Number of Shares |  | Weighted Average Exercise Price Per Share |  | Weighted Average Remaining Contractual Term (years) |  | Aggregate Intrinsic Value
| (In thousands, except per share amounts)
Outstanding as of December 31, 2013 | 11,377,146 |  |  | $ | 11.32 |  |  |  |  |  |
Options granted | 1,797,462 |  |  | $ | 8.78 |  |  |  |  |  |
Options exercised | (206,843 | ) |  | $ | 6.73 |  |  |  |  |  |
Options forfeited | (269,083 | ) |  | $ | 15.20 |  |  |  |  |  |
Outstanding as of March 31, 2014 | 12,698,682 |  |  | $ | 10.95 |  |  | 6.13 |  | $ | 36,153 |
Vested or expected to vest at March 31, 2014 | 11,752,766 |  |  | $ | 11.25 |  |  | 5.91 |  | $ | 32,643 |
Options exercisable at March 31, 2014 | 6,303,547 |  |  | $ | 14.94 |  |  | 3.74 |  | $ | 10,850 |
Weighted-average assumptions for Stock Option Plans | The following table presents the weighted-average assumptions used to estimate the fair value of stock options granted that contain only service conditions in the periods presented.
| Stock Option Plans
| Three Months Ended
| March 31,
| 2014 |  | 2013
Stock Option Plans |  |  |  |  |
Expected stock price volatility | 44 | % |  | 47 | %
Risk free interest rate | 2.1 | % |  | 0.9 | %
Expected term (in years) | 6.1 |  |  | 5.4 |
Weighted-average fair value of stock options granted to employees | $ | 3.92 |  |  | $ | 2.33 |
Schedule of nonvested equity stock and stock units activity | The following table reflects the activity related to nonvested equity stock and stock units for the three months ended March 31, 2014:
Nonvested Equity Stock and Stock Units |  | Shares |  | Weighted- Average Grant-Date Fair Value
Nonvested at December 31, 2013 |  | 629,649 |  |  | $ | 8.56 |
Granted |  | 205,808 |  |  | $ | 8.79 |
Vested |  | (117,828 | ) |  | $ | 9.56 |
Forfeited |  | (13,078 | ) |  | $ | 6.67 |
Nonvested at March 31, 2014 |  | 704,551 |  |  | $ | 8.49 |

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