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Summary of Significant Accounting Policies - Net loss per share (Details) - shares | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Net Loss per Share |  |  |
Warrants outstanding (in shares) | 39,474 | 39,474 |
Anti-dilutive securities | 9,199,512 | 6,869,189 | 5,207,582
Stock options |  |  |
Net Loss per Share |  |  |
Anti-dilutive securities | 8,342,429 | 6,112,948 | 4,720,772
Unvested restricted stock units |  |  |
Net Loss per Share |  |  |
Anti-dilutive securities | 817,609 | 716,767 | 447,336
Warrants |  |  |
Net Loss per Share |  |  |
Anti-dilutive securities | 39,474 | 39,474 | 39,474
Exchange Warrants |  |  |
Net Loss per Share |  |  |
Warrants outstanding (in shares) | 2,575,000 |  |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257 + Details
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