Statement of Financial Position [Abstract] Cash and cash equivalents Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Investment securities – available for sale, at fair value Total Short-term Investments Accrued interest receivable on investment securities Advances, deposits and other current assets Total current assets Property and equipment (at cost, less accumulated depreciation of $1,957,517 and $1,633,517, respectively) Accumulated depreciation (in Dollars) Finite-Lived Intangible Assets by Major Class [Axis] In Process Research and Development [Member] Finite lived intangible assets, net In-process research and development (Note 7) Goodwill Goodwill (Note 7) Deposits, deferred fees and other assets Patents [Member] Total other assets Total assets Accounts payable – trade Other accrued liabilities Total Accrued Liabilities Notes payable – current portion Deferred revenue – current portion Total current liabilities Earn–out milestone liability Earn-out milestone liability (Note 12) Common stock warrant liability Common Stock Warrant Liability Common Stock Warrant Liability Common Stock Warrant Liability Notes payable – non-current portion Deferred revenue – non-current portion Other liabilities - non-current Total liabilities Preferred stock, $0.01 par value: 100,000 shares authorized; no shares issued or outstanding at September 30, 2015 and December 31, 2014, respectively Preferred stock, par value (in Dollars per share) Preferred stock, shares authorized Preferred stock, shares issued Preferred stock, shares outstanding Common stock, $0.01 par value; 75,000,000 shares authorized; 23,111,603 and 20,097,603 shares issued at September 30, 2015 and December 31, 2014, and 23,027,988 and 19,984,203 shares outstanding at September 30, 2015 and December 31, 2014, respectively Common stock, par value (in Dollars per share) Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common stock, shares outstanding Additional paid-in capital Accumulated other comprehensive loss Balance at January 1, 2015 Balance at September 30, 2015 Accumulated deficit Subtotal Treasury stock, at cost (83,615 and 113,400 shares at September 30, 2015 and December 31, 2014, respectively) Treasury stock, shares Total stockholders' equity Total liabilities and stockholders' equity Income Statement [Abstract] Licensing revenue Research and development General and administrative Acquisition costs Total operating expenses Loss from operations Gain (loss) from change in valuation of common stock warrant liability Gain (Loss) from Change in Valuation of Common Stock Warrant Liability Gain from valuation of earn-out milestone liability Investment income, net Investment income, net Interest expense Other (expense) income Total other (expense) income, net Net loss Basic and diluted (in Dollars per share) Basic and diluted (in Shares) Statement of Comprehensive Income [Abstract] Net loss Net loss Realized (gain) loss on investment securities recognized in investment income, net Realized loss reclassified from other accumulated comprehensive loss Unrealized gain (loss) on investment securities Other comprehensive gain (loss) Net other comprehensive loss, net Comprehensive loss Statement of Cash Flows [Abstract] Depreciation and amortization Change in fair value of common stock warrant liability Change in fair value of earn-out milestone liability Increase (Decrease) in Other Operating Assets Deferred revenue Stock-based compensation Shares issued out of treasury Amortization of deferred finance charges and debt discount associated with notes payable Change in deferred rent liability Loss realized on sale of investment securities Accrued interest on short term investments Prepaid expenses, deposits and other assets Accounts payable - trade Accrued liabilities Net cash used in operating activities Purchases of investment securities Proceeds from sale and maturity of investment securities Cash used in acquisition of EGEN, Inc. assets, net of cash received Cash, net of cash acquired Refund on security for letter of credit Purchases of property and equipment Net cash provided by (used in) investing activities Proceeds from sale of common stock equity, net of issuance costs Proceeds from Issuance of Common Stock (in Dollars) Proceeds from note payable Principal payments on notes payable Net cash provided by financing activities Decrease in cash and cash equivalents Fair value of common stock issued in acquisition of EGEN, Inc. assets Interest paid Disclosure Text Block [Abstract] Earnings Per Share [Abstract] Investments, Debt and Equity Securities [Abstract] Short-term Investment by Bond Maturities [Abstract] Investment Type [Axis] Certificate of Deposit [Member] Short-term investments, Cost Short-term investments, Fair Value Short-term investments available for sale bonds – corporate issuances Corporate Debt Securities [Member] Investment Maturing Within 3 Months [Member] Short-term investments maturities, Cost Short-term investments maturities, Fair Value Investment Maturing Between 3 and 12 Months [Member] Investment Securities Gross Unrealized Losses and Fair Value by Investment Category [Abstract] Major Types of Debt and Equity Securities [Axis] Short-term investments with unrealized gains Short-term investments with unrealized gains Short-term investments with unrealized losses Short-term investments with unrealized losses Total Investment Income [Abstract] Interest and dividends accrued and paid Accretion of investment premium Realized losses Component of Accumulated Other Comprehensive Loss [Abstract] Equity Components [Axis] Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Unrealized gains on investment securities Fair Value Disclosures [Abstract] Assets and Liabilities at Fair Value on a Recurring Basis [Abstract] Measurement Frequency [Axis] Fair Value, Measurements, Recurring [Member] Fair Value, Measurements, Nonrecurring [Member] Common stock warrant liability (Note 13) Fair Value, Hierarchy [Axis] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Business Combinations [Abstract] Fair Value of Consideration [Abstract] Celsion common stock (2,712,188 shares valued at $3.48 which was the last closing price of our common stock at the time of closing the transaction on June 20, 2014) Common Stock, shares issued Stock Issued During Period, Shares, Acquisitions (in Shares) Common Stock, price per share (in Dollars per share) Share Price (in Dollars per share) Holdback Shares (670,070 shares of Celsion common stock which were discounted by 38% to reflect the cost of the restriction) Common Stock, shares to be issued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares (in Shares) Common Stock, discount Earn-out Payments (at fair value*) Business Combination, Consideration Transferred, Liabilities Incurred Total fair value of consideration Business Combination, Consideration Transferred Business Acquisition [Axis] EGEN, Inc. [Member] Summary of Estimated Fair Values of Acquired Assets and Liabilities [Abstract] Property and equipment, net In-process research and development Total assets Accounts payable and accrued liabilities Net assets acquired Pro Forma Information [Abstract] Revenues Loss from operations Net loss applicable to common shareholders Payables and Accruals [Abstract] Accrued Liabilities [Abstract] Amounts due to Contract Research Organizations and other contractual agreements Contractual Obligation Accrued payroll and related benefits Accrued professional fees Accrued interest on notes payable Other Debt Disclosure [Abstract] Future Principal Payments Due on the Credit Agreement [Abstract] For the year period ending September 30, 2016 For the year period ending September 30, 2017 Total Debt Instrument [Axis] Hercules Credit Agreement [Member] Stockholders' Equity Note [Abstract] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Fair Value of Option Assumptions [Abstract] Award Type [Axis] Employee Stock Option [Member] Risk-free interest rate Expected volatility Expected life (in years) Expected forfeiture rate Expected dividend yield Range [Axis] Minimum [Member] Maximum [Member] Stock Option and Restricted Stock Awards [Abstract]