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Stock-based compensation (Tables) | 9 Months Ended
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Sep. 30, 2022
Share-Based Payment Arrangement [Abstract] |
Schedule of Stock Option Activity Under Plan | A summary of stock option activity is as follows:
| Number of Shares |  | Weighted- Average Exercise Price
Outstanding at January 1, 2022 | 8,342,429 |  |  | $ | 11.25 |
Granted | 2,765,034 |  |  | 5.41 |
Exercised | (54,299) |  |  | 3.81 |
Cancelled | (528,384) |  |  | 13.33 |
Outstanding at September 30, 2022 | 10,524,780 |  |  | $ | 9.65 |
Vested and expected to vest at September 30, 2022 | 10,524,780 |  |  | $ | 9.65 |
Exercisable at September 30, 2022 | 5,339,351 |  |  | $ | 8.96 |
Schedule of Restricted Stock Activity | A summary of the RSU activity is as follows:
| Number of Shares
Unvested at January 1, 2022 | 817,609 |
Granted | 1,379,849 |
Vested | (190,841) |
Forfeited | (135,935) |
Unvested at September 30, 2022 | 1,870,682 |
Schedule of Stock-Based Compensation Expense by Award Type | The following table presents stock-based compensation expense by award type included within the Company’s condensed consolidated statements of operations and comprehensive loss:
| Three Months Ended September 30, |  | Nine Months Ended September 30,
(in thousands) | 2022 |  | 2021 |  | 2022 |  | 2021
Stock options | $ | 3,901 |  |  | $ | 3,986 |  |  | $ | 11,952 |  |  | $ | 10,617 |
Restricted stock units | 1,365 |  |  | 881 |  |  | 3,832 |  |  | 2,636 |
Employee stock purchase plan | 109 |  |  | 61 |  |  | 424 |  |  | 296 |
Stock-based compensation expense included in total operating expenses | $ | 5,375 |  |  | $ | 4,928 |  |  | $ | 16,208 |  |  | $ | 13,549 |
Schedule of Stock-Based Compensation Expense as Reflected in the Company's Condensed Consolidated Statements of Operations and Comprehensive Loss | The following table presents stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss:
| Three Months Ended September 30, |  | Nine Months Ended September 30,
(in thousands) | 2022 |  | 2021 |  | 2022 |  | 2021
Research and development | $ | 2,890 |  |  | $ | 2,607 |  |  | $ | 8,569 |  |  | $ | 7,410 |
General and administrative | 2,485 |  |  | 2,321 |  |  | 7,639 |  |  | 6,139 |
Stock-based compensation expense included in total operating expenses | $ | 5,375 |  |  | $ | 4,928 |  |  | $ | 16,208 |  |  | $ | 13,549 |
Schedule of Weighted Average Assumptions for Estimating Fair Value of Option Awards | The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2022 |  | 2021 |  | 2022 |  | 2021
Risk-free interest rate | 2.9 | % |  | 1.0 | % |  | 2.0 | % |  | 0.8 | %
Expected dividend yield | — | % |  | — | % |  | — | % |  | — | %
Expected term (years) | 6.11 |  | 6.11 |  | 5.99 |  | 6.05
Expected stock price volatility | 94 | % |  | 82 | % |  | 88 | % |  | 83 | %

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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 https://asc.fasb.org/extlink&oid=128089324&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 https://asc.fasb.org/extlink&oid=128089324&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 https://asc.fasb.org/extlink&oid=128089324&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 https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901 + Details
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