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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2018
Stock-Based Compensation |
Schedule of total employee, director and non-employee stock-based compensation expense recognized |
|  | Three Months Ended |  | Nine Months Ended
|  | September 30, |  | September 30,
|  | 2018 |  | 2017 |  | 2018 |  | 2017
General and administrative |  | $ | 2,732 |  | $ | 1,422 |  | $ | 6,037 |  | $ | 4,305
Research and development |  |  | 3,388 |  |  | 2,183 |  |  | 9,436 |  |  | 5,906
|  | $ | 6,120 |  | $ | 3,605 |  | $ | 15,473 |  | $ | 10,211
|  | Three Months Ended |  | Nine Months Ended
|  | September 30, |  | September 30,
|  | 2018 |  | 2017 |  | 2018 |  | 2017
Stock options |  | $ | 5,832 |  | $ | 3,462 |  | $ | 14,723 |  | $ | 9,820
ESPP |  |  | 209 |  |  | 143 |  |  | 562 |  |  | 391
Restricted stock units |  |  | 79 |  |  | — |  |  | 188 |  |  | —
|  | $ | 6,120 |  | $ | 3,605 |  | $ | 15,473 |  | $ | 10,211
Summary of stock option activity |
|  |  |  | Weighted |  | Weighted |  |
|  |  |  | Average |  | Average |  |
|  | Number of |  | Exercise |  | Remaining |  | Aggregate
|  | Shares subject |  | Price |  | Contractual |  | Intrinsic
|  | to outstanding |  | (Per |  | Term |  | Value
|  | options |  | Share) |  | (in years) |  | (in thousands)
Balances at December 31, 2017 |  | 5,093,442 |  | $ | 15.32 |  |  | 7.62 |  |  |
Options granted |  | 1,679,400 |  | $ | 26.63 |  |  |  |  |  |
Options forfeited |  | (107,720) |  | $ | 21.66 |  |  |  |  |  |
Options exercised |  | (788,409) |  | $ | 8.96 |  |  |  |  |  |
Balance at September 30, 2018 |  | 5,876,713 |  | $ | 19.29 |  |  | 7.70 |  | $ | 115,992
Exercisable |  | 2,857,873 |  | $ | 14.76 |  |  | 6.56 |  | $ | 69,180
Schedule of weighted average assumptions used for estimation of fair value of stock options |
|  | Options |  | Options |
|  | Three Months Ended |  | Nine Months Ended |
|  | September 30, |  | September 30, |
|  | 2018 |  | 2017 |  | 2018 |  | 2017 |
Expected term (years) |  | 6.1 |  | 6.1 |  | 6.1 |  | 6.1 |
Expected volatility |  | 72.8 | % | 96.7 | % | 73.1 | % | 89.8 | %
Risk-free interest rate |  | 2.87 | % | 1.95 | % | 2.56 | % | 2.03 | %
Expected dividend yield |  | — | % | — | % | — | % | — | %
Schedule of weighted average assumptions used for estimation of fair value of ESPP |
|  | ESPP |  | ESPP |
|  | Three Months Ended |  | Nine Months Ended |
|  | September 30, |  | September 30, |
|  | 2018 |  | 2017 |  | 2018 |  | 2017 |
Expected term (years) |  | 0.5 - 2.0 |  | 0.5 - 2.0 |  | 0.5 - 2.0 |  | 0.5 - 2.0 |
Expected volatility |  | 61.2 - 71.4 | % | 67.8 - 79.8 | % | 61.2 - 71.4 | % | 67.8 - 79.8 | %
Risk-free interest rate |  | 1.47 - 2.41 | % | .47 - 1.09 | % | 1.47 - 2.41 | % | .47 - 1.09 | %
Expected dividend yield |  | — | % | — | % | — | % | — | %
Summary of restricted stock unity activity |
|  |  |  | Weighted
|  | Restricted |  | Average Grant
|  | Stock |  | Date Fair Value
|  | Units |  | (Per unit)
Unvested at December 31, 2017 |  | — |  | $ | —
Granted |  | 33,933 |  | $ | 27.64
Vested |  | — |  | $ | —
Forfeited |  | — |  | $ | —
Unvested at September 30, 2018 |  | 33,933 |  | $ | 27.64

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