Document And Entity Information Note To Financial Statement Details Textual Significant Accounting Policies Note 3 - Short Term Investments Available for Sale Note 4 - Fair Values of Financial Instruments Note 5 - Acquisition of EGEN, Inc. 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Note 5 - Acquisition of Egen, Inc. - Amortization Schedule for Covenant Not to Complete (Details) Note 6 - Property and Equipment - Property, Plant, and Equipment Useful Life (Details) Fair value us-gaap_AvailableForSaleSecurities Short-term investments, fair value Note 6 - Property and Equipment - Property, Plant, and Equipment Useful Life (Details) (Parentheticals) Note 7 - Other Accrued Liabilities - Other Accrued Liabilities (Details) Certificate of Deposit [Member] Savings certificate entitling the bearer to receive interest. Note 9 - Income Taxes - Reconciliation of the Statutory Tax Rate to the Effective Rate (Details) Note 9 - Income Taxes - Components of the Deferred Tax Asset (Details) Note 9 - Income Taxes - Operating Loss Carry Forwards (Details) Note 11 - Stock-based Compensation - Stock Option Activity (Details) Note 11 - Stock-based Compensation - Non-vested Restricted Stock Awards (Details) Note 11 - Stock-based Compensation - Stock Options Outstanding (Details) Pre-Funded Series BB Warrant [Member] Information relating to Pre-Funded Series BB Warrant. Note 11 - Stock-based Compensation - Fair Value of Option Assumptions (Details) Note 12 - Earn-out Milestone Liability - Summary of the Changes in the Earn-out Milestone Liability (Details) Note 13 - Warrants - Summary of Warrant Activity (Details) Series AA Warrant [Member] Information relating to Series AA warrants. Note 17 - Contingent Liabilities and Commitments - Summary of the Future Minimum Payments Required Under Leases (Details) Investment Maturing Between 3 and 12 Months [Member] Maturity of short-term investment. Notes To Financial Statements Investment Maturing Within Three Months [Member] Maturity of investment. Notes To Financial Statements [Abstract] clsn_ClassOfWarrantOrRightOfferedPriceOfWarrantsOrRights Class of Warrant or Right, Offered Price of Warrants or Rights Offered price per share or per unit of warrants or rights. Short-term investments with unrealized gains, fair value Available for sale securities with continuous gain position less than 12 months fair value. 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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. 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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First Fifty Percent [Member] Represents first 50% of a warrant issued. Hercules Warrant [Member] Represents Hercules Technology Growth Capital, Inc.. Second Fifty Percent [Member] Represents second fifty percent of a warrant issued. 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Pre-Funded Series CCC Warrants [Member] Represents the information pertaining to the Pre-Funded Series CCC Warrants. Non-cash items included in net loss: Intangible Assets Disclosure [Text Block] 2013 Warrants, 2014 Warrants, and June 2016 Warrants [Member] Represents the information pertaining to the 2013 Warrants, 2014 Warrants, and June 2016 Warrants. Entity Central Index Key clsn_BeneficialOwnershipPercentageThreshold Beneficial Ownership Percentage Threshold Beneficial ownership percentage threshold for purchase of shares of company's common stock. Entity Registrant Name 2015 Warrants [Member] Represents the information pertaining to the 2015 Warrants. Entity [Domain] Series DDD Warrants [Member] Represents the information pertaining to Series DDD Warrants. Legal Entity [Axis] Class of Warrant or Right [Domain] clsn_ClassOfWarrantOrRightExercisablePeriod Class of Warrant or Right, Exercisable Period The period in which the warrants or rights are exercisable. us-gaap_ClassOfWarrantOrRightOutstanding Class of Warrant or Right, Outstanding Warrants outstanding (in shares) Warrants outstanding (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 Other current assets Stock Incentive Plan 2007 [Member] Represents Celsion Corporation 2007 Stock Incentive Plan that was adopted in 2007. 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Series C Warrant [Member] Represents information about Series C Warrant. clsn_ContractualObligationReductionThirtyOneMonthsFromInitialTerm Contractual Obligation Reduction Thirty One Months from Initial Term Represents the reduction of the contractual obligation that will occur thirty-one months from the initial term. 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. 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