Significant Accounting Policies (Policies)	3 Months Ended
Significant Accounting Policies (Policies)	Mar. 31, 2020
Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of Armata and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated. The accompanying unaudited consolidated financial statements of the Company should be read in conjunction with the audited financial statements and accompanying notes thereto as of and for the year ended December 31, 2019 included in the Company’s Form 10-K, filed with the U.S. Securities and Exchange Commission on March 19, 2020. The accompanying unaudited financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial statements. Any reference in the Notes to applicable guidance is meant to refer to authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). In the opinion of management, the accompanying consolidated financial statements include all adjustments that are of a normal and recurring nature and that are necessary for the fair presentation of the Company’s financial position and the results of its operations and cash flows for the periods presented. Interim results are not necessarily indicative of results for the full year or any future period.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in its consolidated financial statements and accompanying notes. On an ongoing basis, management evaluates these estimates and judgments, which are based on historical and anticipated results and trends, and on various other assumptions that management believes to be reasonable under the circumstances. By their nature, estimates are subject to an inherent degree of uncertainty and, as such, actual results may differ from management’s estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of cash equivalents, other current assets, accounts payable, and accrued liabilities approximate fair value because of the short-term nature of these instruments.
In-Process Research and Development (“IPR&D”) and Acquired IPR&D	In-Process Research and Development (“IPR&D”) IPR&D assets are intangible assets with indefinite lives and are not subject to amortization. The Company’s IPR&D assets represent capitalized incomplete research projects that the Company acquired through the Merger. Such assets are initially measured at their acquisition-date fair values and are subject to impairment testing at least annually until completion or abandonment of research and development efforts associated with the projects. Upon successful completion of each project, the Company makes a determination as to the then remaining useful life of the intangible asset and begins amortization.
Goodwill	Goodwill Goodwill, which has an indefinite useful life, represents the excess of purchase consideration over fair value of net assets acquired. The Company’s goodwill as of March 31, 2020 is associated with AmpliPhi’s business prior to the Merger. Goodwill is not subject to amortization and is required to be tested for impairment at least on an annual basis. The Company tests goodwill for impairment as of December 31 of each year. The Company determines whether goodwill may be impaired by comparing the carrying value of the single reporting unit, including goodwill, to the fair value of the reporting unit. If the fair value is less than the carrying amount, a more detailed analysis is performed to determine whether goodwill is impaired. The impairment loss, if any, is measured as the excess of the carrying value of the goodwill over the implied fair value of the goodwill and is recorded in the Company’s consolidated statements of operations.
Derivative Liabilities	Derivative Liabilities Derivative liabilities are accounted for in accordance with the applicable accounting guidance provided in ASC 815 – Derivatives and Hedging based on the specific terms of the agreements. Derivative liabilities are recorded at fair value at each reporting period with any change in fair value recognized as a component of change in fair value of asset acquisition derivative liability in the consolidated statements of operations. The Company has a zero derivative liability balance at March 31, 2020 as the liability of $1.1 million at December 31, 2018 was settled upon the Merger in May 2019.
Basic and Diluted Net Loss per Share	Basic and Diluted Net Loss per Share Net earnings or loss per share (“EPS”) is calculated in accordance with the applicable accounting guidance provided in ASC 260, Earnings per Share. The Company uses the two-class method for the computation and presentation of net income (loss) per common share attributable to common stockholders. The two-class method is an earnings allocation formula that calculates basic and diluted net income (loss) per common share for each class of common stock separately based on dividends declared and participation rights in undistributed earnings as if all such earnings had been distributed during the period. Under the two-class method, warrants issued to Innoviva in connection with the Private Placement (Note 2) is assumed to participate in undistributed earnings on an as-exercised basis, in accordance with the warrant agreement. Undistributed net losses are allocated entirely to common shareholders since the participating security has no contractual obligation to share in the losses. Accordingly, basic income or loss per share is calculated by dividing net income or loss by the weighted-average number of common shares outstanding, or using the two-class method, whichever is more dilutive. Diluted net income loss per share is computed using the more dilutive of the treasury stock method which reflects the potential dilution that would occur if securities or other contracts to issue common stock were exercised or converted to common stock, or the two-class method. The calculation of diluted loss per share requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the warrants, and the presumed exercise of such securities are dilutive to net loss per share for the period, an adjustment to net loss available to common stockholders used in the calculation is required to remove the change in fair value of the warrants from the numerator for the period. Likewise, an adjustment to the denominator is required to reflect the related dilutive shares, if any, under the treasury stock method.
Grants and Awards	Grants and Awards In applying the provisions of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”), Armata has determined that grants and awards are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as there is not considered to be a transfer of control of goods or services. With respect to each grant or award, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). To the extent the grant or award is within the scope of ASC 808, the Company recognizes amounts received as a contra-expense, as opposed to revenue, on the consolidated statement of operations when the related research and development expenses are incurred. Armata also considers the guidance in ASC Topic 730, Research and Development (“ASC 730”), which requires an assessment, at the inception of the grant or award, of whether the agreement is a liability. If Armata is obligated to repay funds received regardless of the outcome of the related research and development activities, then Armata is required to estimate and recognize that liability. Alternatively, if Armata is not required to repay the funds, then payments received are recorded as a contra-expense as the expenses are incurred. Deferred award liability represents award funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.
Research and Development Expenses	Research and Development Expenses Research and development (“R&D”) costs consist primarily of direct and allocated salaries, incentive compensation, stock-based compensation and other personnel-related costs, facility costs, and third-party services. Third-party services include studies and clinical trials conducted by clinical research organizations. R&D activities are expensed as incurred. The Company records accruals for estimated ongoing clinical trial expenses. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Judgments and estimates are made in determining the accrued balances at the end of the reporting period.
Recent Accounting Pronouncements Not Yet Adopted and Recently Adopted Accounting Standards	Recent Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. The standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that aren’t measured at fair value through net income. For available-for-sale debt securities, entities will be required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities will no longer be permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. This new guidance is effective for calendar-year smaller reporting public entities in the first quarter of 2023. The Company is currently evaluating the impact of this ASU and does not expect that adoption of this standard will have a material impact on its consolidated financial statements or related disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (“ASC 740”), which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intra-period tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. The guidance is effective for calendar-year public business entities in 2021 and interim periods within that year. Early adoption is permitted. The Company does not expect adoption of this new guidance will have a material impact on its consolidated financial statements or related disclosures. Recently Adopted Accounting Standards In November 2018, FASB issued ASU 2018-18, Clarifying the Interaction between Topic 808 and Topic 606. The objective of the standard is to clarify the interaction between Topic 808, Collaborative Arrangements, and Topic 606, Revenue from Contracts with Customers. Currently, Topic 808 does not provide comprehensive recognition or measurement guidance for collaborative arrangements, and the accounting for those arrangements is often based on an analogy to other accounting literature or an accounting policy election. Similarly, aspects of Topic 606 have resulted in uncertainty in practice about the effect of the revenue standard and credit loss standard on the accounting for collaborative arrangements. The standard became effective for the Company for fiscal periods beginning on January 1, 2020. The adoption of this ASU did not have an impact on the Company’s financial condition, results of operations, cash flows, or financial statement disclosures.