Summary of Stock-Based Compensation Expense and Stock Option Activity |
The following table reflects the Company's stock-based compensation expense related to share-based awards for the three and nine months ended September 30, 2019 and 2018: | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended September 30, | | Nine Months Ended September 30, | | Unamortized Expense | | Weighted Average Remaining Expense Period (Years) | ($ in thousands) | 2019 | | 2018 | | 2019 | | 2018 | | At September 30, 2019 | Stock options | $ | 1,469 |
| | $ | 3,957 |
| | $ | 4,691 |
| | $ | 8,587 |
| | $ | 9,225 |
| | 2.5 | Restricted stock units | 4,714 |
| | 11,835 |
| | 14,851 |
| | 21,734 |
| | 35,926 |
| | 2.0 | Employee stock purchase plan | 443 |
| | 296 |
| | 1,162 |
| | 884 |
| | 295 |
| | 0.2 | Total | $ | 6,626 |
| | $ | 16,088 |
| | $ | 20,704 |
| | $ | 31,205 |
| | $ | 45,446 |
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The following summarizes stock option activity for the nine months ended September 30, 2019: | | | | | | | | | | | | | | | Number of Options | | Weighted Average Exercise Price | | Aggregate Intrinsic Value (in thousands) | | Weighted Average Remaining Contractual Term (Years) | Outstanding at December 31, 2018 | 3,077,624 |
| | $ | 39.16 |
| | | | | Granted | 125,640 |
| | 93.16 |
| | | | | Exercised | (1,192,397 | ) | | 34.68 |
| | $ | 99,206 |
| | | Forfeited / Expired | (124,198 | ) | | 50.58 |
| | | | | Outstanding at September 30, 2019 | 1,886,669 |
| | $ | 44.84 |
| | $ | 226,571 |
| | 5.6 | Vested, September 30, 2019 | 1,447,398 |
| | $ | 38.25 |
| | $ | 183,351 |
| | 4.8 | Vested or expected to vest, September 30, 2019 (1) | 1,835,967 |
| |
| | $ | 222,101 |
| | |
(1)Represents total outstanding stock options as of September 30, 2019, adjusted for estimated forfeitures.
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Summary of Restricted Stock Units Activity |
The following table summarizes activity for the Company’s restricted stock units during the nine months ended September 30, 2019: | | | | | | | | | Number of Shares | | Weighted Average Fair Value | Outstanding at December 31, 2018 | 752,207 |
| | $ | 55.02 |
| Granted | 317,212 |
| | 94.68 |
| Vested | (317,481 | ) | | 45.29 |
| Forfeited | (69,013 | ) | | 67.34 |
| Outstanding at September 30, 2019 | 682,925 |
| | $ | 76.72 |
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