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v3.19.1

Preferred Stock - Additional Information (Detail) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
May 31, 2017 USD ($) $ / shares shares | Feb. 29, 2016 shares | May 31, 2015 shares | Sep. 30, 2014 shares | Dec. 31, 2018 USD ($) $ / shares shares | Dec. 31, 2017 USD ($) $ / shares shares | Aug. 28, 2017
Class Of Stock [Line Items] |  |  |  |  |  |  |
Exchange ratio of common stock |  |  |  |  |  |  | 0.5532
Preferred stock, conversion basis |  |  |  |  | one-for-one |  |
Preferred stock, conversion percentage |  |  |  |  | 100.00% |  |
Total consideration from stock sold and issued to investors | $ |  |  |  |  |  | $ 40,433,000 |
Preferred stock dividends declared |  |  |  |  | $ 0 | $ 0 |
Preferred stock dividends paid |  |  |  |  | 0 | 0 |
Preferred stock, par value |  |  |  |  | 0.001 | $ 0.001 |
Public offering price per share threshold for conversion of preferred stock |  |  |  |  | $ 12.09 |  |
Aggregate proceeds threshold for conversion of preferred stock | $ |  |  |  |  | $ 50,000,000 |  |
Preferred stock, shares issued | shares |  |  |  |  | 0 | 0 |
Letter Agreement | The Gates Foundation |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Minimum percentage of initial public offering over price paid upon redemption |  |  |  |  |  | 200.00% |
Private Synlogic |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Preferred stock, par value |  |  |  |  | $ 0.0001 |  |
Series C Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Stock sold and issued to investors | shares | 2,882,679 |  |  |  |  |  |
Stock sold and issued to investors, per share | $ 8.06 |  |  |  |  |  |
Total consideration from stock sold and issued to investors | $ | $ 40,400,000 |  |  |  |  |  |
Offering costs | $ | $ 1,600,000 |  |  |  |  |  |
Series A Preferred Stock |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Vote of preferred stock holders required for approval |  |  |  |  | 70.00% |  |
Series A Preferred Stock | Letter Agreement | The Gates Foundation |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |
Stock sold and issued to investors | shares |  | 361,884 | 218,646 | 201,163 |  |  |
Preferred stock, shares issued | shares |  |  |  | 781,693 |  |  |
Proceeds from issuance of stock to be spend on research | $ |  |  |  |  |  | $ 5,000,000 |

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