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Organization and Principal Activities - Additional Information (Details) $ / shares in Units, $ in Thousands |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
May 14, 2020 USD ($) $ / shares shares | Sep. 30, 2020 USD ($) shares | Jun. 30, 2020 shares | Sep. 30, 2020 USD ($) Segment | Dec. 31, 2019 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Date of incorporation |  |  |  | Apr. 21, 2003 |
Headquartered in |  |  |  | South San Francisco |
Headquartered in state |  |  |  | CA |
Number of operating segments | Segment |  |  |  | 1 |
Net proceeds from issuance of common stock |  |  |  | $ 108,250 |
Accumulated deficit |  | $ 168,329 |  | 168,329 | $ 195,745
Unrestricted cash, cash equivalents and marketable securities |  | 202,400 |  | $ 202,400 |
Substantial doubt about going concern, within one year |  |  |  | false |
Minimum |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Period from issuance date of unaudited interim condensed financial statements |  |  |  | 1 year |
Common Stock |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Shares of common stock | shares |  |  | 12,650,000 |  |
At-the-Market (“ATM") |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Gross proceeds from issuance of common stock |  | 17,400 |  |  |
Underwriting discounts and commissions and other offering expenses |  | 600 |  |  |
Net proceeds from issuance of common stock |  | $ 16,800 |  |  |
At-the-Market (“ATM") | Common Stock |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Shares of common stock | shares |  | 2,000,000 |  |  |
Public Offering |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Gross proceeds from issuance of common stock | $ 98,000 |  |  |  |
Underwriting discounts and commissions and other offering expenses | 6,600 |  |  |  |
Net proceeds from issuance of common stock | $ 91,400 |  |  |  |
Public Offering | Common Stock |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Shares of common stock | shares | 12,650,000 |  |  |  |
Public offering price per share | $ / shares | $ 7.75 |  |  |  |
Underwriters’ Option to Purchase Shares | Common Stock |  |  |  |  |
Organization Consolidation And Presentation Of Financial Statements [Line Items] |  |  |  |  |
Shares of common stock | shares | 1,650,000 |  |  |  |

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