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Equity Plans - Narrative (Details) - shares |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Jan. 01, 2021 | May 31, 2018 | Jul. 31, 2016 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020
Equity Plans |  |  |  |  |  |  |  |
Average volatility | 50.00% |  |  |  |  |  |  | 75.00%
Percentage of volatility of stock options since IPO | 50.00% |  |  |  |  |  |  | 25.00%
2016 Plan |  |  |  |  |  |  |  |
Equity Plans |  |  |  |  |  |  |  |
Expiration period |  |  | 10 years |  |  |  |  |
Number of shares available for issuance |  |  |  | 524,762 |  | 524,762 |  |
2018 Inducement Plan |  |  |  |  |  |  |  |
Equity Plans |  |  |  |  |  |  |  |
Expiration period |  | 10 years |  |  |  |  |  |
Number of shares available for issuance |  |  |  | 243,125 |  | 243,125 |  |
Options to purchase common stock |  |  |  |  |  |  |  |
Equity Plans |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate |  |  |  | 0.00% | 0.00% | 0.00% | 0.00% |

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- Definition Represents the percentage of average volatility for comparable publicly traded biopharmaceutical companies over a period equal to the expected term of the stock option grants, used in the calculation of expected volatility. + References No definition available. + Details
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- Definition Represents the percentage of volatility of stock price since its initial public offering used in the calculation of expected volatility. + References No definition available. + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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 (a)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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