Description of the Business	3 Months Ended
Mar. 31, 2019
Accounting Policies [Abstract]
Description of the Business	1. Description of the Business Gossamer Bio, Inc. (including its subsidiaries, referred to as “we,” “us,” “our,”, or the “Company”) is a clinical-stage biopharmaceutical company focused on discovering, acquiring, developing and commercializing therapeutics in the disease areas of immunology, inflammation and oncology. The Company was incorporated in the state of Delaware on October 25, 2015 (originally as FSG Bio, Inc.) and is based in San Diego, California. The condensed consolidated financial statements include the accounts of Gossamer Bio, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions among the consolidated entity have been eliminated in consolidation. Stock Split In January 2019, the board of directors of the Company approved a reverse stock split of the Company’s common stock at a ratio of one for every 4.5 shares previously held. The reverse stock split became effective on January 23, 2019. All share and per share data included in these condensed consolidated financial statements reflect the stock split. Initial Public Offering in February 2019 On February 12, 2019, the Company completed its initial public offering (“IPO”) with the sale of 19,837,500 shares of common stock, including shares of common stock issued upon the exercise in full of the underwriters’ option to purchase additional shares, at a public offering price of $16.00 per share, resulting in net proceeds of $291.3 million, after deducting underwriting discounts, commissions, and offering expenses. In addition, in connection with the completion of the IPO, all of the Company’s outstanding shares of convertible preferred stock were automatically converted into 30,493,460 shares of common stock. Liquidity and Capital Resources The Company has incurred significant operating losses since its inception. As of March 31, 2019, the Company had an accumulated deficit of $186.5 million. From the Company’s inception through March 31, 2019, the Company has funded its operations primarily through equity financings, including the Company’s IPO which closed on February 12, 2019. The Company raised $601.3 million from October 2017 through March 2019 through Series A and Series B Convertible Preferred Stock, convertible note financings, and the completed IPO, after deducting underwriting discounts, commissions, and offering expenses. In addition, the Company received $12.8 million in cash in connection with the January 2018 acquisition of AA Biopharma Inc. The Company expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As a result, the Company will need to raise capital through equity offerings, debt financings other capital sources, including potential collaborations, licenses and other similar arrangements. Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these condensed consolidated financial statements were available to be issued. There can be no assurance that the Company will be successful in acquiring additional funding, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.

Description of the Business

3 Months Ended

Mar. 31, 2019

1. Description of the Business

Gossamer Bio, Inc. (including its subsidiaries, referred to as “we,” “us,” “our,”, or the “Company”) is a clinical-stage biopharmaceutical company focused on discovering, acquiring, developing and commercializing therapeutics in the disease areas of immunology, inflammation and oncology. The Company was incorporated in the state of Delaware on October 25, 2015 (originally as FSG Bio, Inc.) and is based in San Diego, California.

The condensed consolidated financial statements include the accounts of Gossamer Bio, Inc. and its wholly owned subsidiaries. All intercompany balances and transactions among the consolidated entity have been eliminated in consolidation.

Stock Split

In January 2019, the board of directors of the Company approved a reverse stock split of the Company’s common stock at a ratio of one for every 4.5 shares previously held. The reverse stock split became effective on January 23, 2019. All share and per share data included in these condensed consolidated financial statements reflect the stock split.

Initial Public Offering in February 2019

On February 12, 2019, the Company completed its initial public offering (“IPO”) with the sale of 19,837,500 shares of common stock, including shares of common stock issued upon the exercise in full of the underwriters’ option to purchase additional shares, at a public offering price of $16.00 per share, resulting in net proceeds of $291.3 million, after deducting underwriting discounts, commissions, and offering expenses.

In addition, in connection with the completion of the IPO, all of the Company’s outstanding shares of convertible preferred stock were automatically converted into 30,493,460 shares of common stock.

Liquidity and Capital Resources

The Company has incurred significant operating losses since its inception. As of March 31, 2019, the Company had an accumulated deficit of $186.5 million. From the Company’s inception through March 31, 2019, the Company has funded its operations primarily through equity financings, including the Company’s IPO which closed on February 12, 2019. The Company raised $601.3 million from October 2017 through March 2019 through Series A and Series B Convertible Preferred Stock, convertible note financings, and the completed IPO, after deducting underwriting discounts, commissions, and offering expenses. In addition, the Company received $12.8 million in cash in connection with the January 2018 acquisition of AA Biopharma Inc. The Company expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As a result, the Company will need to raise capital through equity offerings, debt financings other capital sources, including potential collaborations, licenses and other similar arrangements. Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these condensed consolidated financial statements were available to be issued. There can be no assurance that the Company will be successful in acquiring additional funding, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.