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 and deposits on clinical programs Other current assets Property and equipment (at cost, less accumulated depreciation and amortization of $1,633,517 and $1,264,190, respectively) Total Accumulated depreciation (in Dollars) Less accumulated depreciation and amortization Finite-Lived Intangible Assets by Major Class [Axis] In Process Research and Development [Member] In-process research and development In-process research and development (Note 5) Goodwill Goodwill (Note 5) Security deposit on letter of credit Deferred financing fees Other assets Total assets Accounts payable ─ trade Other accrued liabilities Total 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 Note payable – non-current portion Deferred revenue – non-current portion Other liabilities – noncurrent Total liabilities Commitments and contingencies Preferred Stock - $0.01 par value (100,000 shares authorized and no shares issued or outstanding at December 31, 2014 and 2013, 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; 20,097,603 and 13,737,970 shares issued at December 31, 2014 and 2013 and 19,984,203 and 13,604,975 shares outstanding at December 31, 2014 and 2013, respectively) Common Stock, Value, Issued Common stock, par value (in Dollars per share) Common Stock, Par or Stated Value Per Share (in Dollars per share) Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Additional paid-in capital Accumulated other comprehensive loss Accumulated deficit Retained Earnings (Accumulated Deficit) Treasury stock, at cost (113,400 and 132,995 shares at December 31, 2014 and 2013, respectively) Treasury stock, shares Total stockholders’ equity Balance at December 31 Balance at December 31 Total liabilities and stockholders’ equity Income Statement [Abstract] Licensing revenue Research and development General and administrative Acquisition costs Business Combination, Acquisition Related Costs Total operating expenses Operating Expenses Loss from operations Gain (loss) from valuation of common stock warrant liability Gain from valuation of earn-out milestone liability Investment income (loss), net Interest expense Other income (expense) Total other (expense) income Net loss Net loss Net loss Non-cash deemed dividend from beneficial conversion feature on convertible preferred stock Non-cash deemed dividend from beneficial conversion feature on convertible preferred stock Net loss attributable to common shareholders Net loss per common share – basic and diluted (in Dollars per share) Weighted average common shares outstanding – basic and diluted (in Shares) Statement of Comprehensive Income [Abstract] Realized loss on investment securities recognized in investment income, net Unrealized (loss) gain on investment securities Other comprehensive income Comprehensive loss Statement of Cash Flows [Abstract] Depreciation and amortization Change in fair value of common stock warrant liability Gain from the adjustment for the change in fair value included in net income Change in fair value of earn-out milestone liability Increase (Decrease) in Other Operating Assets Cash received for non-refundable research and development fee Deferred revenue Stock based compensation Shares issued out of treasury Amortization of deferred finance charges and debt discount associated with note payable Amortization of patent license fee Change in deferred rent liability Loss realized on sale of investment securities Interest receivable on investments Prepaid expenses and other current assets Deposits and other assets Accounts payable Other 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., 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) by investing activities Proceeds from sale of preferred stock, net of issuance costs Proceeds from sale of common stock equity, net of issuance costs Proceeds from Issuance of Common Stock (in Dollars) Proceeds from exercise of common stock warrants Proceeds from Warrant Exercises (in Dollars) Proceeds from Warrant Exercises Proceeds from exercise of common stock options Proceeds from Stock Options Exercised (in Dollars) Proceeds from note payable Principal payments on note payable Net cash provided by financing activities Increase (decrease) in cash and cash equivalents Interest Statement of Stockholders' Equity [Abstract] Balance at December 31 (in Shares) Balance at December 31 (in Shares) Shares, Outstanding Unrealized gain on investments available for sale Valuation Technique [Axis] Series A Redeemable Convertible Preferred Stock [Member] Valuation of common stock warrants in connection with notes payable Class of Warrant or Right [Axis] Common Stock Warrants (Member) Conversion of convertible securities Conversion of convertible securities (in Shares) Conversion of Stock, Shares Issued Conversion of Stock, Shares Issued (in Shares) Stock-based compensation expense Allocated Share-based Compensation Expense (in Dollars) Issuance of restricted stock and option exercise Issuance of restricted stock and option exercise (in Shares) Issuance of common stock out of treasury Issuance of common stock out of treasury (in Shares) Stock issued, new issues Stock Issued During Period, Value, New Issues (in Dollars) Stock issued, new issues (in Shares) Stock Issued During Period, Shares, New Issues Non-cash dividend on beneficial conversion feature associated with the preferred stock offering Class of Stock [Axis] Preferred Stock [Member] Sale of Stock [Axis] Direct and ATM [Member] Classification of warrants to/from common stock warrant liability, net Fractional share payment Fractional share payment (in Shares) Common stock issued in connection with the acquisition of EGEN, Inc. assets 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 issued in connection with the acquisition of EGEN, Inc. assets (in Shares) Common Stock, shares issued Stock Issued During Period, Shares, Acquisitions Hercules Warrant [Member] Equity Components [Axis] Preferred Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Treasury Stock [Member] Accumulated Other Comprehensive Income (Loss) [Member] Retained Earnings [Member] Accounting Policies [Abstract] Financial Condition [Abstract] Investments, Debt and Equity Securities [Abstract] Short-Term Investment by Bond Maturities [Abstract] Investment Type [Axis] Certificate of Deposit [Member] Short-term investments Short-term investments Short-term investments available for sale Bonds – corporate issuances Available-for-sale Securities Corporate Debt Securities [Member] Investment Maturing Within 3 Months [Member] Short-term investments maturities Short-term investments maturities Investment Maturing Between 3 and 12 Months [Member] Investment Income [Abstract] Interest and dividends accrued and paid Accretion of investment premium Losses on investment maturity and sales, net 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 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 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]