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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Stock-Based Compensation |
Summary of stock option activity |
|  |  |  | Weighted |  | Weighted
|  |  |  | Average |  | Average
|  |  |  | Exercise |  | Remaining
|  |  |  | Price |  | Contractual
|  | Shares |  | Per Share |  | Term (In Years)
Options outstanding at December 31, 2019 |  | 1,699,202 |  | $ | 44.87 |  | 8.0
Granted |  | 1,512,675 |  | $ | 10.53 |  |
Exercised |  | (78,259) |  | $ | 4.57 |  |
Canceled |  | (91,389) |  | $ | 41.86 |  |
Options outstanding at December 31, 2020 |  | 3,042,229 |  | $ | 28.93 |  | 8.2
Options vested and expected to vest at December 31, 2020 |  | 2,881,532 |  | $ | 30.04 |  | 8.2
Options exercisable at December 31, 2020 |  | 907,982 |  | $ | 76.39 |  | 6.2
Shares available for grant under the 2008 Plan |  | 898,977 |  |  |  |  |
Summary of restricted stock activity |
|  |  |  | Weighted
|  |  |  | Average
|  |  |  | Grant Date
|  |  |  | Fair Value
|  | Shares |  | (per share)
Outstanding and unvested at December 31, 2019 |  | 1,110 |  | $ | 34.83
Granted |  | — |  | $ | —
Vested |  | (1,110) |  | $ | 34.83
Canceled |  | — |  | $ | —
Outstanding and unvested at December 31, 2020 |  | — |  | $ | —
Schedule of stock-based compensation expense |
|  | 2020 |  | 2019 |  | 2018
|  | (In thousands)
Research and development |  | $ | 1,933 |  | $ | 2,053 |  | $ | 3,874
General and administrative |  |  | 1,982 |  |  | 2,498 |  |  | 4,207
Total stock-based compensation expense |  | $ | 3,915 |  | $ | 4,551 |  | $ | 8,081
Schedule of assumptions used for the fair value of employee stock options granted |
|  | 2020 |  | 2019 |  | 2018
Expected stock price volatility |  | 91 - 98% |  | 90 - 91% |  | 73 - 85%
Expected option term |  | 6.0 Years |  | 6.0 Years |  | 6.0 Years
Risk-free interest rate |  | 0.5 - 0.7% |  | 1.6 - 2.5% |  | 2.8 - 3.1%
Expected dividend yield |  | None |  | None |  | None

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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + 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=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 S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901 + 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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- 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=116856206&loc=d3e5070-113901 + Details
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