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Equity Plans - Narrative (Details) - shares | 1 Months Ended | 12 Months Ended |  |
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Jul. 31, 2016 | Dec. 31, 2020 | Dec. 31, 2018 | Dec. 31, 2019 | May 31, 2018
Equity Plans |  |  |  |  |
Average volatility |  | 75.00% |  |  |
Percentage of volatility of stock options since IPO |  | 25.00% |  |  |
2007 Stock Option and Incentive Plan |  |  |  |  |
Equity Plans |  |  |  |  |
Number of shares available for issuance | 0 |  |  |  |
2016 Equity Incentive Plan |  |  |  |  |
Equity Plans |  |  |  |  |
Number of shares authorized | 1,200,000 |  |  |  |
Maximum annual additional authorized shares as a percentage of outstanding shares |  | 4.00% |  |  |
Number of shares available for issuance |  |  |  | 538,374 |
2016 Equity Incentive Plan | Stockholders possessing more than 10% of the total combined voting power | Minimum |  |  |  |  |
Equity Plans |  |  |  |  |
Exercise price as a percentage of the fair market value of common stock on grant date |  | 110.00% |  |  |
2016 Equity Incentive Plan | Tranche two |  |  |  |  |
Equity Plans |  |  |  |  |
Vesting period | 4 years |  |  |  |
Restricted stock unit incentive awards granted in 2018 |  |  |  |  |
Equity Plans |  |  |  |  |
Expiration period |  | 10 years |  |  |
Vesting period |  |  | 18 months |  |
Number of shares authorized |  |  |  |  | 750,000
Number of shares available for issuance |  | 574,375 |  |  |
Stock options - employees, consultants, directors | 2007 Stock Option and Incentive Plan |  |  |  |  |
Equity Plans |  |  |  |  |
Expiration period |  | 10 years |  |  |
Stock options - employees, consultants, directors | 2007 Stock Option and Incentive Plan | Minimum |  |  |  |  |
Equity Plans |  |  |  |  |
Vesting period |  | 4 years |  |  |
Stock options - employees, consultants, directors | 2016 Equity Incentive Plan |  |  |  |  |
Equity Plans |  |  |  |  |
Expiration period |  | 10 years |  |  |
Stock options - employees, consultants, directors | 2016 Equity Incentive Plan | Minimum |  |  |  |  |
Equity Plans |  |  |  |  |
Exercise price as a percentage of the fair market value of common stock on grant date |  | 100.00% |  |  |
Non Employee Director Initial Stock Options | 2016 Equity Incentive Plan | Maximum |  |  |  |  |
Equity Plans |  |  |  |  |
Vesting period |  | 3 years |  |  |
Nonemployee Director Annual Refresher Stock Options | 2016 Equity Incentive Plan | Minimum |  |  |  |  |
Equity Plans |  |  |  |  |
Vesting period |  | 1 year |  |  |

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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 Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + 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)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + 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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