3.26.1 html 125 235 1 false 45 0 false 6 false false R1.htm 995200090 - Document - Document and Entity Information Sheet http://www.altimmune.com/role/DocumentDocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 995200100 - Statement - CONSOLIDATED BALANCE SHEETS Sheet http://www.altimmune.com/role/StatementConsolidatedBalanceSheets CONSOLIDATED BALANCE SHEETS Statements 2 false false R3.htm 995200105 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical) Sheet http://www.altimmune.com/role/StatementConsolidatedBalanceSheetsParenthetical CONSOLIDATED BALANCE SHEETS (Parenthetical) Statements 3 false false R4.htm 995200200 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS Sheet http://www.altimmune.com/role/StatementConsolidatedStatementsOfOperationsAndComprehensiveLoss CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS Statements 4 false false R5.htm 995200300 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY Sheet http://www.altimmune.com/role/StatementConsolidatedStatementsOfChangesInStockholdersEquity CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY Statements 5 false false R6.htm 995200400 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS Sheet http://www.altimmune.com/role/StatementConsolidatedStatementsOfCashFlows CONSOLIDATED STATEMENTS OF CASH FLOWS Statements 6 false false R7.htm 995210101 - Disclosure - Nature of Business and Basis of Presentation Sheet http://www.altimmune.com/role/DisclosureNatureOfBusinessAndBasisOfPresentation Nature of Business and Basis of Presentation Notes 7 false false R8.htm 995210201 - Disclosure - Summary of Significant Accounting Policies Sheet http://www.altimmune.com/role/DisclosureSummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 8 false false R9.htm 995210301 - Disclosure - Fair Value Measurements Sheet http://www.altimmune.com/role/DisclosureFairValueMeasurements Fair Value Measurements Notes 9 false false R10.htm 995210401 - Disclosure - Accrued Expenses Sheet http://www.altimmune.com/role/DisclosureAccruedExpenses Accrued Expenses Notes 10 false false R11.htm 995210501 - Disclosure - Term Loan Sheet http://www.altimmune.com/role/DisclosureTermLoan Term Loan Notes 11 false false R12.htm 995210601 - Disclosure - Other Noncurrent Liabilities Sheet http://www.altimmune.com/role/DisclosureOtherNoncurrentLiabilities Other Noncurrent Liabilities Notes 12 false false R13.htm 995210701 - Disclosure - Stockholders' Equity Sheet http://www.altimmune.com/role/DisclosureStockholdersEquity Stockholders' Equity Notes 13 false false R14.htm 995210801 - Disclosure - Stock-Based Compensation Sheet http://www.altimmune.com/role/DisclosureStockBasedCompensation Stock-Based Compensation Notes 14 false false R15.htm 995210901 - Disclosure - Net Loss Per Share Sheet http://www.altimmune.com/role/DisclosureNetLossPerShare Net Loss Per Share Notes 15 false false R16.htm 995211001 - Disclosure - Commitments and Contingencies Sheet http://www.altimmune.com/role/DisclosureCommitmentsAndContingencies Commitments and Contingencies Notes 16 false false R17.htm 995211101 - Disclosure - Segment Information Sheet http://www.altimmune.com/role/DisclosureSegmentInformation Segment Information Notes 17 false false R18.htm 995211201 - Disclosure - Subsequent Events Sheet http://www.altimmune.com/role/DisclosureSubsequentEvents Subsequent Events Notes 18 false false R19.htm 995410 - Disclosure - Pay vs Performance Disclosure Sheet http://xbrl.sec.gov/ecd/role/PvpDisclosure Pay vs Performance Disclosure Notes 19 false false R20.htm 995445 - Disclosure - Insider Trading Arrangements Sheet http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements Insider Trading Arrangements Notes 20 false false R21.htm 99920202 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://www.altimmune.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://www.altimmune.com/role/DisclosureSummaryOfSignificantAccountingPolicies 21 false false R22.htm 99930303 - Disclosure - Fair Value Measurements (Tables) Sheet http://www.altimmune.com/role/DisclosureFairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://www.altimmune.com/role/DisclosureFairValueMeasurements 22 false false R23.htm 99930403 - Disclosure - Accrued Expenses (Tables) Sheet http://www.altimmune.com/role/DisclosureAccruedExpensesTables Accrued Expenses (Tables) Tables http://www.altimmune.com/role/DisclosureAccruedExpenses 23 false false R24.htm 99930503 - Disclosure - Term Loan (Tables) Sheet http://www.altimmune.com/role/DisclosureTermLoanTables Term Loan (Tables) Tables http://www.altimmune.com/role/DisclosureTermLoan 24 false false R25.htm 99930603 - Disclosure - Other Noncurrent Liabilities (Tables) Sheet http://www.altimmune.com/role/DisclosureOtherNoncurrentLiabilitiesTables Other Noncurrent Liabilities (Tables) Tables http://www.altimmune.com/role/DisclosureOtherNoncurrentLiabilities 25 false false R26.htm 99930803 - Disclosure - Stock-Based Compensation (Tables) Sheet http://www.altimmune.com/role/DisclosureStockBasedCompensationTables Stock-Based Compensation (Tables) Tables http://www.altimmune.com/role/DisclosureStockBasedCompensation 26 false false R27.htm 99930903 - Disclosure - Net Loss Per Share (Tables) Sheet http://www.altimmune.com/role/DisclosureNetLossPerShareTables Net Loss Per Share (Tables) Tables http://www.altimmune.com/role/DisclosureNetLossPerShare 27 false false R28.htm 99940201 - Disclosure - Summary of Significant Accounting Policies (Detail) Sheet http://www.altimmune.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetail Summary of Significant Accounting Policies (Detail) Details http://www.altimmune.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies 28 false false R29.htm 99940301 - Disclosure - Fair Value Measurements - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) Sheet http://www.altimmune.com/role/DisclosureFairValueMeasurementsScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisDetail Fair Value Measurements - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) Details 29 false false R30.htm 99940302 - Disclosure - Fair Value Measurements - Schedule of Short Term Investments (Detail) Sheet http://www.altimmune.com/role/DisclosureFairValueMeasurementsScheduleOfShortTermInvestmentsDetail Fair Value Measurements - Schedule of Short Term Investments (Detail) Details 30 false false R31.htm 99940303 - Disclosure - Fair Value Measurements- Additional Information (Detail) Sheet http://www.altimmune.com/role/DisclosureFairValueMeasurementsAdditionalInformationDetail Fair Value Measurements- Additional Information (Detail) Details 31 false false R32.htm 99940401 - Disclosure - Accrued Expenses - Schedule of Accrued Expenses and Other Current Liabilities (Detail) Sheet http://www.altimmune.com/role/DisclosureAccruedExpensesScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesDetail Accrued Expenses - Schedule of Accrued Expenses and Other Current Liabilities (Detail) Details 32 false false R33.htm 99940501 - Disclosure - Term Loan (Details) Sheet http://www.altimmune.com/role/DisclosureTermLoanDetails Term Loan (Details) Details http://www.altimmune.com/role/DisclosureTermLoanTables 33 false false R34.htm 99940502 - Disclosure - Term Loan - Summary of term loan (Details) Sheet http://www.altimmune.com/role/DisclosureTermLoanSummaryOfTermLoanDetails Term Loan - Summary of term loan (Details) Details 34 false false R35.htm 99940503 - Disclosure - Term Loan - Future principal loan payments (Details) Sheet http://www.altimmune.com/role/DisclosureTermLoanFuturePrincipalLoanPaymentsDetails Term Loan - Future principal loan payments (Details) Details 35 false false R36.htm 99940601 - Disclosure - Other Noncurrent Liabilities - Summary of other noncurrent liabilities (Detail) Sheet http://www.altimmune.com/role/DisclosureOtherNoncurrentLiabilitiesSummaryOfOtherNoncurrentLiabilitiesDetail Other Noncurrent Liabilities - Summary of other noncurrent liabilities (Detail) Details 36 false false R37.htm 99940701 - Disclosure - Stockholders' Equity - Additional Information (Detail) Sheet http://www.altimmune.com/role/DisclosureStockholdersEquityAdditionalInformationDetail Stockholders' Equity - Additional Information (Detail) Details 37 false false R38.htm 99940801 - Disclosure - Stock-Based Compensation - Additional Information (Detail) Sheet http://www.altimmune.com/role/DisclosureStockBasedCompensationAdditionalInformationDetail Stock-Based Compensation - Additional Information (Detail) Details 38 false false R39.htm 99940802 - Disclosure - Stock-Based Compensation - Schedule of Information Related to Stock Options Outstanding (Detail) Sheet http://www.altimmune.com/role/DisclosureStockBasedCompensationScheduleOfInformationRelatedToStockOptionsOutstandingDetail Stock-Based Compensation - Schedule of Information Related to Stock Options Outstanding (Detail) Details 39 false false R40.htm 99940803 - Disclosure - Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) Sheet http://www.altimmune.com/role/DisclosureStockBasedCompensationScheduleOfStockBasedCompensationExpenseDetail Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) Details 40 false false R41.htm 99940901 - Disclosure - Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) Sheet http://www.altimmune.com/role/DisclosureNetLossPerShareScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDetail Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) Details 41 false false R42.htm 99941001 - Disclosure - Commitments and Contingencies - Additional Information (Detail) Sheet http://www.altimmune.com/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetail Commitments and Contingencies - Additional Information (Detail) Details 42 false false R43.htm 99941201 - Disclosure - Subsequent Events (Detail) Sheet http://www.altimmune.com/role/DisclosureSubsequentEventsDetail Subsequent Events (Detail) Details http://www.altimmune.com/role/DisclosureSubsequentEvents 43 false false All Reports Book All Reports alt-20260331.xsd alt-20260331_cal.xml alt-20260331_def.xml alt-20260331_lab.xml alt-20260331_pre.xml alt-20260331x10q.htm alt-20260331x10q002.jpg http://fasb.org/us-gaap/2024 http://xbrl.sec.gov/dei/2024 http://xbrl.sec.gov/ecd/2024 true true