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Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Summary of Option Activity | The following table summarizes option activity under the Company’s 2004 Plan and 2018 Plan:
|  | Shares |  |  | Weighted- Average Exercise Price |  |  | Weighted- Average Remaining Contract Term (Years) |  |  | Aggregate Intrinsic Value (in thousands) |
Stock options outstanding at December 31, 2019 |  |  | 3,872,664 |  |  | $ | 12.89 |  |  |  | 7.88 |  |  | $ | 2,119 |
Granted |  |  | 1,496,806 |  |  | $ | 8.88 |  |  |  |  |  |  |  |  |
Exercised |  |  | (14,194 | ) |  | $ | 4.50 |  |  |  |  |  |  |  |  |
Canceled and forfeited |  |  | (46,037 | ) |  | $ | 10.58 |  |  |  |  |  |  |  |  |
Stock options outstanding at June 30, 2020 |  |  | 5,309,239 |  |  | $ | 11.80 |  |  |  | 8.03 |  |  | $ | 1,286 |
Stock options exercisable at June 30, 2020 |  |  | 2,226,316 |  |  | $ | 12.53 |  |  |  | 6.74 |  |  | $ | 630 |
Schedule of Employee Stock Options Valuation | For determining stock-based compensation expense, the fair-value-based measurement of each employee stock option was estimated as of the date of grant using the Black-Scholes option-pricing model with assumptions as follows:
|  | Six Months Ended |
|  | June 30, |
|  | 2020 |  |  | 2019 |
Expected term (in years) |  | 2.84-7.01 |  |  | 5.03-7.01 |
Expected volatility |  | 73.15%-83.96% |  |  | 72.89%-74.89% |
Risk-free interest rate |  | 0.16%-1.62% |  |  | 1.85%-2.55% |
Expected dividend |  |  | – |  |  |  | – |
Summary of Status and Activity of Non-vested RSUs | A summary of the status and activity of non-vested RSUs at June 30, 2020 is as follows:
|  | Number of shares |  |  | Weighted Average Grant-Date Fair Value |
Non-vested December 31, 2019 |  |  | 335,799 |  |  | $ | 13.49 |
Granted |  |  | 497,250 |  |  | $ | 8.19 |
Vested and released |  |  | (41,300 | ) |  | $ | 11.44 |
Canceled and forfeited |  |  | (16,758 | ) |  | $ | 9.64 |
Non-vested June 30, 2020 |  |  | 774,991 |  |  | $ | 10.28 |
Schedule of Fair Value of ESPP Shares Using Option Pricing Model | For the six months ended June 30, 2020, the fair value of ESPP shares was estimated using the following assumptions:
| Six Months Ended |
| June 30, |
| 2020 |  |  | 2019 |
Expected term (in years) | 0.5 |  |  | 0.5 |
Expected volatility |  | 63.04 | % |  |  | 74.41 | %
Risk-free interest rate |  | 1.92 | % |  |  | 2.09 | %
Expected dividend |  | – |  |  |  | – |
Schedule of Stock-Based Compensation Expense Recognized | Total stock-based compensation expense recognized was as follows:
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
|  | 2020 |  |  | 2019 |  |  | 2020 |  |  | 2019 |
|  | (in thousands) |  |  | (in thousands) |
Research and development expense: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock options |  | $ | 340 |  |  | $ | 246 |  |  | $ | 584 |  |  | $ | 474 |
Restricted stock units |  |  | 243 |  |  |  | 196 |  |  |  | 407 |  |  |  | 303 |
ESPP |  |  | 113 |  |  |  | - |  |  |  | 220 |  |  |  | 76 |
Subtotal |  |  | 696 |  |  |  | 442 |  |  |  | 1,211 |  |  |  | 853 |
General and administrative expense: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock options |  |  | 1,756 |  |  |  | 1,654 |  |  |  | 3,458 |  |  |  | 3,154 |
Restricted stock units |  |  | 528 |  |  |  | 367 |  |  |  | 989 |  |  |  | 714 |
ESPP |  |  | 31 |  |  |  | - |  |  |  | 60 |  |  |  | 28 |
Subtotal |  |  | 2,315 |  |  |  | 2,021 |  |  |  | 4,507 |  |  |  | 3,896 |
Total |  | $ | 3,011 |  |  | $ | 2,463 |  |  | $ | 5,718 |  |  | $ | 4,749 |
Summary of the Status of Call Options | A summary of the status of the call options at June 30, 2020 and at December 31, 2019 is as follows:
|  | June 30, |  |  | December 31, |
|  | 2020 |  |  | 2019 |
|  | Shares |  |  | Shares |
Options vested and exercised |  |  | 191,165 |  |  |  | 191,165 |
Options vested and outstanding |  |  | 66,685 |  |  |  | - |
Options unvested and outstanding |  |  | 8,890 |  |  |  | 75,475 |
Total options granted |  |  | 266,740 |  |  |  | 266,640 |

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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year. + 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + 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 (d) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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