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Stockholders' Equity (Tables) | 6 Months Ended
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Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Summary of Stock-Based Compensation Expense | Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
|  | 2019 |  |  | 2018 |  |  | 2019 |  |  | 2018 |
Research and development |  | $ | 464 |  |  | $ | 390 |  |  | $ | 866 |  |  | $ | 713 |
General and administrative |  |  | 781 |  |  |  | 606 |  |  |  | 1,460 |  |  |  | 1,118 |
Total stock-based compensation expense |  | $ | 1,245 |  |  | $ | 996 |  |  | $ | 2,326 |  |  | $ | 1,831 |
Schedule of Estimated Fair Value of Stock Options Granted | The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company’s equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented:
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
|  | 2019 |  |  | 2018 |  |  | 2019 |  |  | 2018 |
Equity Incentive Plans |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected term (in years) |  |  | 5.70 |  |  |  | 5.70 |  |  |  | 5.99 |  |  |  | 5.95 |
Expected volatility |  |  | 78 | % |  |  | 84 | % |  |  | 81 | % |  |  | 85 | %
Risk-free interest |  |  | 2.05 | % |  |  | 2.79 | % |  |  | 2.50 | % |  |  | 2.73 | %
Dividend yield |  |  | 0 | % |  |  | 0 | % |  |  | 0 | % |  |  | 0 | %
2016 ESPP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected term (in years) |  |  | — |  |  |  | — |  |  |  | 0.49 |  |  |  | 0.49 |
Expected volatility |  |  | — |  |  |  | — |  |  |  | 66 | % |  |  | 69 | %
Risk-free interest |  |  | — |  |  |  | — |  |  |  | 2.55 | % |  |  | 2.00 | %
Dividend yield |  |  | — |  |  |  | — |  |  |  | 0 | % |  |  | 0 | %

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- Definition Tabular disclosure of the amount of total share-based compensation cost, including the amounts attributable to each share-based compensation plan and any related tax benefits. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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