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Equity Incentive Plans (Tables) | 6 Months Ended
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Jun. 30, 2021
Share-based Payment Arrangement [Abstract] |
Summary of Activity Related to Stock Option Awards | A summary of the activity related to stock option awards during the six months ended June 30, 2021 is as follows:
| Shares Subject to Options |  | Weighted-Average Exercise Price per Share |  | Weighted-Average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value (in thousands)
Outstanding at January 1, 2021 | 2,920,700 |  |  | $ | 26.67 |  |  |  |  |
Granted | 1,037,374 |  |  | $ | 29.52 |  |  |  |  |
Exercises | (77,034) |  |  | $ | 9.86 |  |  |  |  |
Forfeitures and cancellations | (149,232) |  |  | $ | 29.47 |  |  |  |  |
Outstanding at June 30, 2021 | 3,731,808 |  |  | $ | 27.70 |  |  | 7.51 |  | $ | 24,823 |
Exercisable at June 30, 2021 | 1,744,975 |  |  | $ | 27.82 |  |  | 5.76 |  | $ | 17,109 |
Summary of Weighted Average Assumptions used to Estimate Fair Value | The estimated fair values of stock option awards granted to employees were determined on the date of grant using the Black-Scholes option valuation model with the following weighted-average assumptions:
| Six Months Ended June 30, |
| 2021 |  | 2020 |  |  |
Risk-free interest rate |  | 0.7 | % |  |  | 1.2 | % |  |  |  |
Expected volatility |  | 93.1 | % |  |  | 91.8 | % |  |  |  |
Expected dividend yield |  | — |  | % |  |  | — |  | % |  |  |  |
Expected term (in years) |  | 6.18 |  |  |  | 6.25 |  |  |  |  |
Weighted-average grant date fair value per share | $ | 22.39 |  |  | $ | 11.97 |  |  |  |  |
Summary of Non-cash Stock-based Compensation Expense | Total non-cash stock-based compensation expense for all stock awards that was recognized in the consolidated statements of operations and comprehensive loss is as follows:
| Three Months Ended June 30, |  | Six Months Ended June 30,
(in thousands) | 2021 |  | 2020 |  | 2021 |  | 2020
Research and development | $ | 1,435 |  |  | $ | 958 |  |  | $ | 2,629 |  |  | $ | 2,104 |
General and administrative | 2,255 |  |  | 1,783 |  |  | 4,376 |  |  | 3,612 |
Total | $ | 3,690 |  |  | $ | 2,741 |  |  | $ | 7,005 |  |  | $ | 5,716 |

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- Definition Tabular disclosure of cost recognized for award under share-based payment arrangement by plan. Includes, but is not limited to, related tax benefit. + 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=120381028&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=120381028&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=120381028&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=120381028&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=120381028&loc=d3e5070-113901 + Details
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