Description of the Business	3 Months Ended
Description of the Business	Mar. 31, 2021
Accounting Policies [Abstract]
Description of the Business	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. Liquidity and Capital Resources The Company has incurred significant operating losses since its inception. As of March 31, 2021, the Company had an accumulated deficit of $635.2 million. From the Company’s inception through March 31, 2021, the Company has funded its operations primarily through equity and debt financings. The Company raised $942.0 million from October 2017 through March 31, 2021 through Series A and Series B convertible preferred stock financings, a convertible note financing, its initial public offering, or IPO, its Credit Facility (as defined in Note 5 below), and concurrent underwritten public offerings of its 5.00% convertible senior notes due 2027 (the “2027 Notes”) and common stock in May 2020. See Note 5 for additional information regarding the Credit Facility and the 2027 Notes. 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 and 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. COVID-19 The COVID-19 pandemic has caused significant business disruption around the globe. The extent of the impact of COVID-19 on the Company’s operational and financial performance will depend on certain developments, including the duration and spread of the pandemic and the impact on the Company’s clinical trials, employees and vendors. At this point, the degree to which COVID-19 has impacted and may continue to impact the Company’s financial condition or results of operations is uncertain. A prolonged pandemic could have a material and adverse impact on financial results and business operations of the Company, including the timing and ability of the Company to complete certain clinical trials and other efforts required to advance the development of its product candidates and raise additional capital. For example, certain sites temporarily closed enrollment in the Company's Phase 1b clinical trial in pulmonary arterial hypertension ("PAH") in 2020 as a result of the ongoing COVID-19 pandemic. In addition, due to the challenges of enrolling patients worldwide posed by the COVID-19 pandemic, the Company may experience delays in enrollment of patients in its Phase 2 clinical trials of GB004 in ulcerative colitis and of seralutinib, also known as GB002, in PAH, as well as delays in reporting data results from its ongoing trials.