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Certificate of Deposit [Member] Savings certificate entitling the bearer to receive interest. us-gaap_NotesPayable Notes Payable Pre-Funded Series BB Warrant [Member] Information relating to Pre-Funded Series BB Warrant. Series AA Warrant [Member] Information relating to Series AA warrants. Investment Maturing Within Three Months [Member] Maturity of investment. Fair Value, Inputs, Level 1 [Member] Proceeds from exercise of common stock warrants Proceeds from Warrant Exercises Fair Value, Inputs, Level 3 [Member] Lawrenceville New Jersey [Member] Information pertaining to property located in Lawrenceville, New Jersey. 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June 2016 Common Stock Offering [Member] The Securities Purchase Agreement classified as "June 2016 Purchase Agreement" made the Company with an investor. clsn_ContractualObligationRemaining Contractual Obligation Remaining The remaining amount due under contractual obligations. Series D Warrant [Member] Represents information about Series D Warrant. clsn_ContractualObligationReductionNineteenMonthsFromInitialTerm Contractual Obligation Reduction Nineteen Months from Initial Term Represents the reduction of the contractual obligation that will occur nineteen months from initial term. Accrued liabilities clsn_OwnershipPercentageRestrictionThresholdForWarrantExercise Ownership Percentage, Restriction Threshold for Warrant Exercise Represents the ownership restriction threshold for a holder to exercise warrant. clsn_OperatingLeasesMonthlyRentPaymentInFirstYear Operating Leases, Monthly Rent Payment in First Year Represents the payment to be paid each month in the first year under an operating lease. clsn_OperatingLeasesMonthlyRentPaymentInFinalYear Operating Leases, Monthly Rent Payment in Final Year Represents the payment to be paid each month in the final year under an operating lease. clsn_NumberOfDaysNoticeRequirementToIncreaseOrDecreaseBeneficialOwnershipLimitation Number of Days Notice Requirement to Increase or Decrease Beneficial Ownership Limitation Represents the number of days notice requirement to increase or decrease beneficial ownership limitation. clsn_ClassOfWarrantOrRightTerm Class of Warrant or Right, Term Period of time the warrants or rights are issued, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. clsn_MaximumBeneficialOwnershipOfThePurchaser Maximum Beneficial Ownership of the Purchaser Represents the maximum beneficial ownership of the Purchaser. clsn_ReductionOfEscrowDeposit Reduction of Escrow Deposit Represents the reduction of the escrow deposit. 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Licensing Transaction [Text Block] The entire disclosure for a contractual arrangement, in which the Company gave another party an exclusive license. clsn_WarrantsExercisablePeriod Warrants Exercisable Period Represents the period in which warrants are initially exercisable. clsn_OperatingLeasesMonthlyRentPayment Operating Leases, Monthly Rent Payment Represents the payment to be paid each month under an operating lease. Basis of Accounting [Text Block] clsn_DeferredRevenueAmortizationPeriod Deferred Revenue Amortization Period The amortization period for deferred revenue. Hisun [Member] Represents Zhejiang Hisun Pharmaceutical Co. Ltd. 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Statement of Cash Flows [Abstract] Warrants [Text Block] The entire disclosure for warrant liabilities. us-gaap_RepaymentsOfNotesPayable Principal payments on notes payable us-gaap_RepaymentsOfLinesOfCredit Repayments of Lines of Credit us-gaap_StockIssuedDuringPeriodSharesAcquisitions Stock Issued During Period, Shares, Acquisitions us-gaap_AllocatedShareBasedCompensationExpense Allocated Share-based Compensation Expense EGEN Inc [Member] Information pertaining to the business acquisition of EGEN, Inc. Ovarian Cancer Study Milestone [Member] Earnout payments that will become payable upon achieving certain specified development milestones relating to an EGEN-001 ovarian cancer study to be conducted by Celsion or its subsidiary. us-gaap_ProceedsFromLinesOfCredit Proceeds from Lines of Credit TheraSilence Technology Milestone [Member] Earnout payments that will become payable upon achieving certain specified development milestones relating to the TheraSilence technology acquired from EGEN. Nature of Operations [Text Block] Glioblastoma Multiforme Brain Cancer Study Milestone [Member] Earnout payments that will become payable upon achieving certain specified development milestones relating to an EGEN-001 glioblastoma multiforme brain cancer study to be conducted by Celsion or its subsidiary. Hercules Credit Agreement [Member] Represents a loan agreement with Hercules Technology Growth Capital, Inc. (“Hercules”). 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Expected dividend yield clsn_ShelfRegistrationStatementAmount Shelf Registration Statement Amount Shelf Registration statement. Interest and dividends accrued and paid Investment income, net Investment income, net us-gaap_GoodwillAcquiredDuringPeriod Goodwill, Acquired During Period Risk-free interest rate Schedule of Milestone Risk Adjustment Assessment [Table Text Block] Tabular disclosure of the risk-adjustment assessment of each milestone. Expected volatility us-gaap_OperatingIncomeLoss Loss from operations Deferred revenue – current portion Business Combination Disclosure [Text Block] Expected life (in years) (Year) us-gaap_LegalFees Legal Fees Treasury stock, shares (in shares) Amendment Flag Aggregate intrinsic value of outstanding awards, non-vested restricted stock Common stock - $0.01 par value (112,500,000 shares authorized; 55,471,171 and 31,226,336 shares issued at March 31, 2017 and December 31, 2016, respectively and 55,466,492 and 31,221,657 shares outstanding at March 31, 2017 and December 31, 2016, respectively) clsn_CommonStockOfferingPeriodOfRestriction Common Stock Offering Period of Restriction Represents period after the closing of common stock offering during which the Company is prohibited from effecting or entering into an agreement to issue common stock or any other securities that are at any time convertible into, or exercisable or exchangeable for, or otherwise entitle the holder thereof to receive, common stock to the extent such issuance or sale involves certain variable conversion, exercise or exchange prices or such agreement provides for sale of securities at a price to be determined in the future. 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Current Fiscal Year End Date clsn_CommissionOnProceedsFromAtmSharesPercent Commission on Proceeds from ATM Shares Percent Commission on Proceeds from ATM Shares, Percent Equity awards exercisable, contractual term (Year) Aggregate intrinsic value of awards exercisable, options Series A Warrant [Member] Series A Convertible Preferred Stock (Member) clsn_AggregateOfferingPrice Aggregate Offering Price Represents maximum aggregate offering price for shares of common stock that the Company may offer and sell through a sales agent. Document Fiscal Period Focus Document Fiscal Year Focus Advances, deposits and other current assets Document Period End Date Series B Warrant [Member] Information relating to Series B warrants. Preferred Stock - $0.01 par value (100,000 shares authorized and no shares issued or outstanding at March 31, 2017 and December 31, 2016, respectively) Accretion of investment premium us-gaap_FiniteLivedIntangibleAssetUsefulLife Finite-Lived Intangible Asset, Useful Life Preferred stock, shares issued (in shares) Equity awards exercisable, weighted average exercise price (in dollars per share) Document Type Equity awards exercisable, options (in shares) us-gaap_DepreciationDepletionAndAmortization Depreciation and amortization Equity awards outstanding, contractual term (Year) Preferred stock, share authorized (in shares) Preferred Stock, Shares Authorized us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Accounts payable - trade Document Information [Line Items] Document Information [Table] Preferred stock, par value (in dollars per share) Accrued payroll and related benefits Other accrued liabilities Total us-gaap_AssetsCurrent Subtotal current assets Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Entity Filer Category us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill) us-gaap_FinitelivedIntangibleAssetsAcquired1 Finite-lived Intangible Assets Acquired Entity Current Reporting Status Counterparty Name [Domain] Entity Voluntary Filers Counterparty Name [Axis] Entity Well-known Seasoned Issuer us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice Equity awards outstanding, weighted average exercise price (in dollars per share) Equity awards outstanding, weighted average exercise price (in dollars per share) us-gaap_IndefinitelivedIntangibleAssetsAcquired Indefinite-lived Intangible Assets Acquired Equity awards forfeited, cancelled or expired, weighted average exercise price (in dollars per share) Other us-gaap_AmortizationOfIntangibleAssets Amortization of Intangible Assets Accrued professional fees Entity Central Index Key Entity Registrant Name us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations Equity awards forfeited, cancelled or expired (in shares) Entity [Domain] Legal Entity [Axis] Class of Warrant or Right [Domain] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber Equity awards outstanding, options (in shares) Equity awards outstanding, options (in shares) us-gaap_ClassOfWarrantOrRightOutstanding Class of Warrant or Right, Outstanding Warrants outstanding (in shares) Warrants outstanding (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod Equity awards forfeited, cancelled or expired (in shares) Class of Warrant or Right [Axis] us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1 Class of Warrant or Right, Exercise Price of Warrants or Rights Warrants outstanding (in dollars per share) Warrants outstanding (in dollars per share) us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight Class of Warrant or Right, Number of Securities Called by Each Warrant or Right us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights Class of Warrant or Right, Number of Securities Called by Warrants or Rights Current liabilities: us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic Net loss Stock Incentive Plan 2007 [Member] Represents Celsion Corporation 2007 Stock Incentive Plan that was adopted in 2007. Entity Common Stock, Shares Outstanding (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Interest paid us-gaap_DeferredFinanceCostsGross Debt Issuance Costs, Gross us-gaap_Assets Total assets us-gaap_PaymentsForRent Payments for Rent Additional paid-in capital Stockholders’ equity: us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Expected forfeiture rate The estimated forfeiture rate of share-based payment awards. us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Trading Symbol Earn-out Milestone Liability Disclosure [Text Block] The disclosure related to earn-out milestone liabilities. us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Purchases of property and equipment Risk-adjustment assessment Risk Adjusted Assessment of Each Milestone The percentage of risk-adjusted assessment of each milestone. 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