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Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Stockholders Equity [Line Items] |  |
Reserved common stock | 8,691,304 | 7,357,234
Common Stock |  |
Stockholders Equity [Line Items] |  |
Reserved common stock | 5,309,239 | 3,872,664
Restricted Common Stock Units Issued and Outstanding |  |
Stockholders Equity [Line Items] |  |
Reserved common stock | 774,991 | 335,799
2004 and 2018 Equity Incentive Plan |  |
Stockholders Equity [Line Items] |  |
Reserved common stock | 1,970,938 | 2,750,416
2018 Employee Stock Purchase Plan |  |
Stockholders Equity [Line Items] |  |
Reserved common stock | 483,066 | 326,542
Warrants to Purchase Common Stock |  |
Stockholders Equity [Line Items] |  |
Reserved common stock | 153,070 | 71,813

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- Definition Aggregate number of common shares reserved for future issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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