Nature of Business and Basis of Presentation	9 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	1. Nature of Business and Basis of Presentation Altimmune, Inc., headquartered in Gaithersburg, Maryland, United States, together with its subsidiaries (collectively, “Altimmune”) is a clinical stage biopharmaceutical company incorporated in 1997 under the laws of the State of Delaware. Altimmune is focused on discovering and developing immunotherapies and vaccines to address significant unmet medical needs. Since its inception, Altimmune has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff, and raising capital, and has financed its operations through the issuance of common and convertible preferred stock, long-term debt, and proceeds from research grants and government contracts. Altimmune has not generated any revenues from the sale of any products to date, and there is no assurance of any future revenues from product sales. Pursuant to an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) dated January 18, 2017, PharmAthene, Inc. (“PharmAthene”), its wholly owned acquisition subsidiaries Mustang Merger Sub Corp I Inc. (“Merger Sub Corp”) and Mustang Merger Sub II LLC (“Merger Sub LLC”) agreed to acquire 100% of the outstanding capital stock of Altimmune in a reverse triangular merger and reorganization pursuant to section 368(a) of the Internal Revenue Code (the “Mergers”) (Note 3). As a condition for the Mergers, in January 2017, prior to the Mergers, Altimmune entered into a Convertible Promissory Note Purchase Agreement (the “Note Agreement”) for the private placement of $8.6 million of 6% convertible notes (the “Notes”) (See Note 7) to be issued in two separate closings. The initial closing dated March 9, 2017 resulted in $3,150,630 of gross proceeds. The initial closing also included $196,496 of certain existing outstanding notes payable and $881,044 of certain accrued expenses that were modified and became a component of the Notes on March 9, 2017. In connection with the Notes, Altimmune issued warrants to purchase 49,776 shares of Altimmune’s common stock to certain noteholders, with an exercise price of $0.01 per share. These warrants are classified as permanent equity (see Note 10). The second closing was included in the sale of Series B redeemable convertible preferred stock (“redeemable preferred stock”) that closed on August 16, 2017 (see Note 9). On May 4, 2017, Altimmune and PharmAthene closed the Mergers in accordance with the terms of the Merger Agreement. Upon the closing of the Mergers, (i) Merger Sub Corp merged with and into Altimmune, with Altimmune remaining as the surviving corporation; (ii) Altimmune then merged with and into Merger Sub LLC, with Merger Sub LLC (renamed as “Altimmune LLC”) remaining as the surviving entity; and (iii) PharmAthene was renamed as “Altimmune, Inc.” Upon closing of the Mergers, all equity instruments of Altimmune were exchanged for corresponding equity instruments of PharmAthene (see Note 3). Altimmune and PharmAthene and its subsidiaries are hereinafter collectively referred to as the “Company” or “we”. The accompanying unaudited condensed consolidated financial statements are prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Accordingly, they do not include all of the information and disclosures required by accounting principles generally accepted in the United States for complete consolidated financial statements and should be read in conjunction with Altimmune’s audited consolidated financial statements for the year ended December 31, 2016 included in the Registration Statement on Form S-4/A which was filed with the SEC on March 31, 2017. In the opinion of management, we have prepared the accompanying unaudited condensed consolidated financial statements on the same basis as our audited consolidated financial statements, and these condensed consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the results of the interim periods presented. The operating results for the interim periods presented are not necessarily indicative of the results expected for the full year 2017 or any future years or periods. The unaudited condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded assets and liabilities that might be necessary should we be unable to continue as a going concern.

1. Nature of Business and Basis of Presentation

Altimmune, Inc., headquartered in Gaithersburg, Maryland, United States, together with its subsidiaries (collectively, “Altimmune”) is a clinical stage biopharmaceutical company incorporated in 1997 under the laws of the State of Delaware. Altimmune is focused on discovering and developing immunotherapies and vaccines to address significant unmet medical needs. Since its inception, Altimmune has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff, and raising capital, and has financed its operations through the issuance of common and convertible preferred stock, long-term debt, and proceeds from research grants and government contracts. Altimmune has not generated any revenues from the sale of any products to date, and there is no assurance of any future revenues from product sales.

Pursuant to an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) dated January 18, 2017, PharmAthene, Inc. (“PharmAthene”), its wholly owned acquisition subsidiaries Mustang Merger Sub Corp I Inc. (“Merger Sub Corp”) and Mustang Merger Sub II LLC (“Merger Sub LLC”) agreed to acquire 100% of the outstanding capital stock of Altimmune in a reverse triangular merger and reorganization pursuant to section 368(a) of the Internal Revenue Code (the “Mergers”) (Note 3).

As a condition for the Mergers, in January 2017, prior to the Mergers, Altimmune entered into a Convertible Promissory Note Purchase Agreement (the “Note Agreement”) for the private placement of $8.6 million of 6% convertible notes (the “Notes”) (See Note 7) to be issued in two separate closings. The initial closing dated March 9, 2017 resulted in $3,150,630 of gross proceeds. The initial closing also included $196,496 of certain existing outstanding notes payable and $881,044 of certain accrued expenses that were modified and became a component of the Notes on March 9, 2017. In connection with the Notes, Altimmune issued warrants to purchase 49,776 shares of Altimmune’s common stock to certain noteholders, with an exercise price of $0.01 per share. These warrants are classified as permanent equity (see Note 10). The second closing was included in the sale of Series B redeemable convertible preferred stock (“redeemable preferred stock”) that closed on August 16, 2017 (see Note 9).

On May 4, 2017, Altimmune and PharmAthene closed the Mergers in accordance with the terms of the Merger Agreement. Upon the closing of the Mergers, (i) Merger Sub Corp merged with and into Altimmune, with Altimmune remaining as the surviving corporation; (ii) Altimmune then merged with and into Merger Sub LLC, with Merger Sub LLC (renamed as “Altimmune LLC”) remaining as the surviving entity; and (iii) PharmAthene was renamed as “Altimmune, Inc.” Upon closing of the Mergers, all equity instruments of Altimmune were exchanged for corresponding equity instruments of PharmAthene (see Note 3). Altimmune and PharmAthene and its subsidiaries are hereinafter collectively referred to as the “Company” or “we”.

The accompanying unaudited condensed consolidated financial statements are prepared pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Accordingly, they do not include all of the information and disclosures required by accounting principles generally accepted in the United States for complete consolidated financial statements and should be read in conjunction with Altimmune’s audited consolidated financial statements for the year ended December 31, 2016 included in the Registration Statement on Form S-4/A which was filed with the SEC on March 31, 2017. In the opinion of management, we have prepared the accompanying unaudited condensed consolidated financial statements on the same basis as our audited consolidated financial statements, and these condensed consolidated financial statements include all adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the results of the interim periods presented. The operating results for the interim periods presented are not necessarily indicative of the results expected for the full year 2017 or any future years or periods.

The unaudited condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded assets and liabilities that might be necessary should we be unable to continue as a going concern.