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Equity Plans (Tables) | 12 Months Ended
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Dec. 31, 2016
Schedule of Activity under Equity Incentive Plans | Activity under the Company’s equity incentive plans is set forth below:
|  |  |  |  |  |  |  | Options Outstanding |
|  | Options Available for Grant |  |  | Options Outstanding |  |  | Weighted- Average Exercise Price Per Share |  |  | Weighted- Average Remaining Contractual Life (years) |  |  | Aggregate Intrinsic Value |
|  |  |  |  |  |  |  |  |  |  |  |  |  | (in thousands) |
Balances at December 31, 2013 |  |  | 70,082 |  |  |  | 284,879 |  |  | $ | 1.10 |  |  |  | 7.92 |  |  |  |  |
Additional options authorized |  |  | 240,425 |  |  |  | — |  |  |  |  |  |  |  |  |  |  |  |  |
Options granted |  |  | (199,519 | ) |  |  | 199,519 |  |  |  | 1.83 |  |  |  |  |  |  |  |  |
Options exercised |  |  | — |  |  |  | (2,548 | ) |  |  | 1.30 |  |  |  |  |  |  |  |  |
Options forfeited |  |  | 5,844 |  |  |  | (5,844 | ) |  |  | 1.13 |  |  |  |  |  |  |  |  |
Balances at December 31, 2014 |  |  | 116,832 |  |  |  | 476,006 |  |  |  | 1.40 |  |  |  | 8.04 |  |  |  |  |
Additional options authorized |  |  | 431,411 |  |  |  | — |  |  |  |  |  |  |  |  |  |  |  |  |
Options granted |  |  | (408,623 | ) |  |  | 408,623 |  |  |  | 1.24 |  |  |  |  |  |  |  |  |
Options exercised |  |  | — |  |  |  | (43,852 | ) |  |  | 1.30 |  |  |  |  |  |  |  |  |
Options forfeited |  |  | 7,599 |  |  |  | (7,599 | ) |  |  | 1.40 |  |  |  |  |  |  |  |  |
Balances at December 31, 2015 |  |  | 147,219 |  |  |  | 833,178 |  |  |  | 1.33 |  |  |  | 8.56 |  |  |  |  |
Additional options authorized |  |  | 1,697,088 |  |  |  | — |  |  |  |  |  |  |  |  |  |  |  |  |
Options granted |  |  | (1,679,979 | ) |  |  | 1,679,979 |  |  |  | 14.24 |  |  |  |  |  |  |  |  |
Options exercised |  |  | — |  |  |  | (119,328 | ) |  |  | 1.28 |  |  |  |  |  |  |  |  |
Balances at December 31, 2016 |  |  | 164,328 |  |  |  | 2,393,829 |  |  | $ | 10.39 |  |  |  | 8.79 |  |  | $ | 27,820 |
Options exercisable – December 31, 2016 |  |  |  |  |  |  | 492,714 |  |  | $ | 5.19 |  |  |  | 7.70 |  |  | $ | 8,286 |
Options vested and expected to vest – December 31, 2016 |  |  |  |  |  |  | 2,369,135 |  |  | $ | 10.37 |  |  |  | 8.79 |  |  | $ | 27,596 |
Schedule of Stock-based Compensation Expense for Employees and Non-employees for Stock Options and the 2016 ESPP | Total stock-based compensation expense recognized for both employees and non-employees for stock options and the 2016 ESPP was as follows (in thousands):
|  | Year Ended December 31, |
|  | 2016 |  |  | 2015 |  |  | 2014 |
Research and development |  | $ | 1,080 |  |  | $ | 39 |  |  | $ | 17 |
General and administrative |  |  | 1,050 |  |  |  | 60 |  |  |  | 25 |
Total stock-based compensation expense |  | $ | 2,130 |  |  | $ | 99 |  |  | $ | 42 |
Employee and Director [Member] |
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions | The fair value of employee and director stock option awards was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:
|  | Year Ended December 31, |
|  | 2016 |  |  | 2015 |  |  | 2014 |
Expected term (in years) |  |  | 4.16 – 5.95 |  |  |  | 5.89 |  |  |  | 6.08 |
Expected volatility |  |  | 62.5 – 64.8 | % |  |  | 59.8 | % |  |  | 64.7 | %
Risk-free interest rate |  |  | 1.27 – 1.79 | % |  |  | 1.57 – 1.58 | % |  |  | 1.89 | %
Dividend yield |  |  | — |  |  |  | — |  |  |  | — |
Non-employees [Member] |
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions | The fair value of the stock options granted was calculated at each reporting date using the Black-Scholes option-pricing model with the following assumptions:
|  | Year Ended December 31, |
|  | 2016 |  |  | 2015 |  |  | 2014 |
Expected term (in years) |  |  | 6.59 –9.97 |  |  |  | 6.8 |  |  |  | 9.4 |
Expected volatility |  |  | 62.5 – 62.8 | % |  |  | 59.8 | % |  |  | 64.7 | %
Risk-free interest rate |  |  | 1.29 – 1.79 | % |  |  | 1.95 | % |  |  | 2.34 | %
Dividend yield |  |  | — |  |  |  | — |  |  |  | — |
2016 Employee Stock Purchase Plan [Member] |
Schedule of Grant-date Fair Value of Stock Option Awards Using Black-Scholes Option Pricing Model Assumptions | The fair value of the rights granted under the 2016 ESPP was calculated using the Black-Scholes option-pricing model with the following assumptions:
|  | Year Ended |
|  | December 31, 2016 |
Expected term (in years) |  |  | 0.60 |
Expected volatility |  |  | 52.48 | %
Risk-free interest rate |  |  | 0.45 | %
Dividend yield |  |  | — |

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