Stock Based Compensation (Tables)
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12 Months Ended |
Dec. 31, 2017 |
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| Share-based Compensation [Abstract] |
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| Schedule of stock-based compensation expense |
Stock-based compensation expense includes stock options and ESPPP shares. The amount of stock based compensation expense recognized for the years ending December 31, 2017, 2016 and 2015 was as follows:
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Year Ended December 31, |
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2017 |
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2016 |
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2015 |
Research and development |
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$ |
156,047 |
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$ |
141,247 |
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$ |
67,021 |
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General and administrative |
|
1,001,205 |
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|
1,553,644 |
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|
327,727 |
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Total stock-based compensation |
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$ |
1,157,252 |
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$ |
1,694,891 |
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$ |
394,748 |
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| Summary of option activity |
A summary of option activity for the years ended December 31, 2017 and 2016 is as follows:
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Options Outstanding |
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Number of shares |
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Weighted average exercise price |
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Grant date fair value of options |
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Weighted average remaining contractual term (in years) |
Balance, January 1, 2016 |
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959,188 |
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$ |
7.68 |
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7.51 |
Granted |
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915,242 |
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$ |
3.35 |
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$ |
2,155,234 |
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Forfeited |
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(25,071 |
) |
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$ |
5.04 |
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Balance, December 31, 2016 |
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1,849,359 |
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$ |
5.57 |
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8.44 |
Granted |
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1,020,377 |
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$ |
0.94 |
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$ |
669,816 |
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Forfeited |
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(46,247 |
) |
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$ |
3.57 |
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Balance, December 31, 2017 |
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2,823,489 |
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$ |
3.93 |
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7.29 |
Vested and expected to vest at December 31, 2017 |
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2,823,489 |
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$ |
3.93 |
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7.29 |
Exercisable at December 31, 2017 |
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1,762,908 |
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$ |
5.02 |
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6.16 |
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| Schedule of fair value assumptions for options |
The assumptions used to determine the grant date fair value of stock options granted to employees and non-employee directors are as follows:
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Year Ended December 31, |
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2017 |
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2016 |
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2015 |
Risk-free interest rate |
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1.85 |
% |
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— |
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2.38 |
% |
|
1.01 |
% |
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— |
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1.93 |
% |
|
1.64 |
% |
|
— |
|
1.97 |
% |
Expected term of options (in years) |
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5.0 |
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— |
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6.25 |
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5.0 |
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— |
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6.25 |
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5.00 |
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— |
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6.25 |
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Expected stock price volatility |
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55 |
% |
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— |
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100.0 |
% |
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80.00 |
% |
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— |
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100.0 |
% |
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70.0 |
% |
Expected annual dividend yield |
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— |
% |
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— |
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— |
% |
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— |
% |
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— |
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— |
% |
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— |
% |
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— |
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— |
% |
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| Schedule of unrecognized compensation expense |
As of December 31, 2017, there was approximately $1,342,072 of total unrecognized compensation expense related to unvested options granted under the Plan to be recognized as follows:
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Year ending December 31, |
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2018 |
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$ |
732,441 |
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2019 |
|
352,657 |
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2020 |
|
188,351 |
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2021 |
|
68,623 |
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$ |
1,342,072 |
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