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Stock Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Common stock |  |  |  |  |
Shares |  |  |  |  |
Exercised (in shares) | (2,992) |  | (2,992) |  |
Employee stock options |  |  |  |  |
Shares |  |  |  |  |
Outstanding, beginning of period (in shares) |  |  | 227,846 |  |
Granted (in shares) |  |  | 1,113,982 |  |
Assumed in Quellis Acquisition (in shares) |  |  | 55,414 |  |
Exercised (in shares) |  | 0 | (2,992) | 0 |
Cancelled or forfeited (in shares) |  |  | (58,344) |  |
Expired (in shares) |  |  | (1,507) |  |
Outstanding, end of period (in shares) | 1,334,399 |  | 1,334,399 |  | 227,846
Vested and exercisable (in shares) | 127,064 |  | 127,064 |  |
Weighted-Average Exercise Price |  |  |  |  |
Outstanding, beginning of period (in dollars per share) |  |  | $ 68.25 |  |
Granted (in dollars per share) |  |  | 16.21 |  |
Assumed in Quellis Acquisition (in dollars per share) |  |  | 1.73 |  |
Exercised (in dollars per share) |  |  | 2.10 |  |
Cancelled or forfeited (in dollars per share) |  |  | 62.08 |  |
Expired (in dollars per share) |  |  | 100.85 |  |
Outstanding at end of year (in dollars per share) | $ 22.43 |  | 22.43 |  | $ 68.25
Vested and Exercisable (in dollars per share) | $ 74.71 |  | $ 74.71 |  |
Weighted Average Remaining Contractual Term (years) |  |  |  |  |
Outstanding |  |  | 9 years 3 months |  | 8 years 1 month 17 days
Vested and Exercisable |  |  | 7 years 4 months 17 days |  |
Aggregate Intrinsic Value |  |  |  |  |
Outstanding | $ 374 |  | $ 374 |  |
Vested and Exercisable | 178 |  | 178 |  |
Stock Incentive Plans |  |  |  |  |
Intrinsic value of options exercised | 38 |  | 38 |  |
Aggregate fair value of options vested | $ 300 | $ 300 | $ 1,300 | $ 1,000 |
Weighted average grant date fair value of options granted (in dollars per share) | $ 6.20 | $ 29.10 | $ 10.15 | $ 22.32 |
Unrecognized compensation expense related to unvested stock option awards | $ 11,800 |  | $ 11,800 |  |
Weighted-average amortization period over which cost is expected to be recognized |  |  | 3 years 1 month 6 days |  |

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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + 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 (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + 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)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + 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)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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