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STOCKHOLDERS’ EQUITY (Details Narrative) - USD ($) |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 03, 2022 | Feb. 28, 2022 | Jan. 10, 2022 | Mar. 31, 2021 | Mar. 19, 2021 | Jan. 22, 2021 | Sep. 08, 2020 | Jun. 22, 2020 | Feb. 27, 2020 | Dec. 04, 2018 | Sep. 30, 2018 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Feb. 28, 2021 | Mar. 12, 2020 | Feb. 28, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shelf registration statement amount |  |  |  |  | $ 100,000,000 |  |  |  |  |  | $ 75,000,000 |  |  |  |  |  |
Reverse Stock Split |  |  |  |  |  |  |  |  |  |  |  |  | On February 28, 2022, the Company effected a 15-for-1 reverse stock split of its common stock which was made effective for trading purposes as of the commencement of trading on March 31, 2022. As of that date, each 15 shares of issued and outstanding common stock and equivalents was consolidated into one share of common stock. All shares have been restated to reflect the effects of the 15-for-1 reverse stock split. In addition, at the market open on March 1, 2022, the Company’s common stock started trading under a new CUSIP number 15117N602 although the Company’s ticker symbol, CLSN, remained unchanged. |  |  |  |
Stockholders equity note changes in capital structure description |  |  |  |  |  |  |  |  |  |  |  |  | To continue listing on The NASDAQ Capital Market, which requires that the Company comply with the applicable listing requirements under NASDAQ Marketplace Rules, which requirements include, among others, a minimum bid price of at least $1.00 per share. On December 2, 2021, the Company received a letter from NASDAQ indicating that the closing bid price of the Company’s Common Stock fell below $1.00 per share for the previous 30 consecutive business days, and that the Company was therefore not in compliance with the minimum bid price requirement for continued inclusion on The NASDAQ Capital Market. The Company had 180 calendar days, until May 31, 2022, to regain compliance with this requirement, which occurs when the closing bid price of the Company’s Common Stock is at least $1.00 per share for a minimum of ten consecutive business days during the 180-day compliance period. |  |  |  |
Reverse stock split common stock outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 5,770,516 |  |  |  |
Common stock, shares outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 5,770,516 | 2,713,402 |  |  |
Warrants |  |  |  |  |  |  |  |  |  |  |  |  | 7,273 |  |  |  | 213,333
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 52,688,946 | $ 22,811,669 |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  |  |  |  |  |  |  |  | $ 48.30 |  |  |  |
Preferred Stock, Shares Issued |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |
Preferred Stock, Par or Stated Value Per Share |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.01 | $ 0.01 |  |  |
Common Stock, Par or Stated Value Per Share |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.01 | $ 0.01 |  |  |
Preferred Stock Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock Shares Outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse Stock Split |  | On February 28, 2022, the Company effected a 15-for-1 reverse stock split of its common stock which was made effective for trading purposes as of the commencement of trading on March 1, 2022. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares outstanding |  | 15 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Price |  |  | $ 285 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share |  |  | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Preferred Stock and Preference Stock |  |  | $ 14,250,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock Value | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds From Issuance Under Placement | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Series A Convertible Redeemable Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Price |  |  | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Issued |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share |  |  | $ 0.01 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Convertible, Conversion Price |  |  | $ 13.65 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Preferred Stock, Shares Issued upon Conversion |  |  | 1,098,901 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Par or Stated Value Per Share |  |  | $ 13.65 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock Shares Outstanding | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Series B Convertible Redeemable Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Price |  |  | $ 300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Shares Issued |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share |  |  | $ 0.01 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock, Convertible, Conversion Price |  |  | $ 15.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Convertible Preferred Stock, Shares Issued upon Conversion |  |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock Voting Rights |  |  | right to cast 3,000 votes per share |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Par or Stated Value Per Share |  |  | $ 15.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Stock Shares Outstanding | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital on DemandTM Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Less than 12 months, unrealized gains, fair value |  |  |  |  |  |  |  |  |  | $ 16,000,000.0 |  |  |  |  |  |  |
Capital on Demand Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  |  |  |  |  |  | 500,000 | 300,000 |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,900,000 | $ 6,200,000 |  |  |
Securities Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  |  | 304,761 |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  |  | $ 4,800,000 |  |  |  |  |  |  |  |
Shares Issued, Price Per Share |  |  |  |  |  |  |  |  | $ 15.75 |  |  |  |  |  |  |  |
Securities Purchase Agreement [Member] | January 2021 Registered Direct Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  | 1,728,395 |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  | $ 35,000,000 |  |  |  |  |  |  |  |  |  |  |
Share Price |  |  |  |  |  | $ 20.25 |  |  |  |  |  |  |  |  |  |  |
Placement agent fee description. |  |  |  |  |  | In connection with the January 2021 Offering, the Company entered into a placement agent agreement with A.G.P./Alliance Global Partners (“AGP,” and together with Brookline Capital Markets, the “January 2021 Placement Agents”) pursuant to which the Company agreed to pay the January 2021 Placement Agents a cash fee equal to 7% of the aggregate gross proceeds raised from the sale of the securities sold in the January 2021 Offering and reimburse the January 2021 Placement Agents for certain of their expenses in an amount not to exceed $82,500. |  |  |  |  |  |  |  |  |  |  |
Securities Purchase Agreement [Member] | March 2021 Registered Direct Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  | 769,230 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  | $ 15,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Share Price |  |  |  | $ 19.50 |  |  |  |  |  |  |  |  |  |  |  |  |
Placement agent fee description. |  |  |  | Placement Agent Agreement”) with AGP, as lead placement agent (together with JonesTrading Institutional Services LLC and Brookline Capital Markets, a division of Arcadia Securities, LLC, serving as co-placement agents, the “March 2021 Placement Agents”), pursuant to which the Company agreed to pay the March 2021 Placement Agents an aggregate cash fee equal to 7% of the aggregate gross proceeds raised from the sale of the securities sold in the offering and reimburse the Placement Agents for certain of their expenses in an amount not to exceed $82,500. |  |  |  |  |  |  |  |  |  |  |  |  |
Exchange Agreements [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right |  |  |  |  |  |  |  |  |  |  |  | 81,111 |  |  |  |  |
Proceeds from Issuance of Warrants |  |  |  |  |  |  |  |  |  |  |  | $ 1,500,000 |  |  |  |  |
Underwriting Agreement [Member] | Underwritten Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  | 177,777 |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  | $ 9,100,000 |  |  |  |  |  |  |  |  |
Shares Issued, Price Per Share |  |  |  |  |  |  |  | $ 56.25 |  |  |  |  |  |  |  |  |
Share Price |  |  |  |  |  |  |  | 52.3125 |  |  |  |  |  |  |  |  |
Underwriting discount price per share |  |  |  |  |  |  |  | $ 3.9375 |  |  |  |  |  |  |  |  |
Payments from sale of nols |  |  |  |  |  |  |  | 7.00% |  |  |  |  |  |  |  |  |
LPC Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  | 26,000,000.0 |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,200,000 |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 6,600,000 |  |  |  |
Warrants |  |  |  |  |  |  |  |  |  |  |  |  | 2,500,000 |  |  |  |
Maximum [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds From Issuance Under Placement | $ 110,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 400,000 |  |  |  |
Warrants |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  | 81,111 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split common stock outstanding |  |  |  |  |  |  |  |  |  |  |  |  | 86,557,736 |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  |  |  |  |  |  |  | 2,975,503 | 1,111,615 |  |  |
Original Warrants [Member] | Securities Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right |  |  |  |  |  |  |  |  | 198,095 |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  |  |  |  | $ 17.25 |  |  |  |  |  |  |  |
Warrant [Member] | Exchange Agreements [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 213,333 |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18.60 |
LPC Commitment Shares [Member] | LPC Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  |  |  |  | 218,854 |  |  |  |  |  |  |  |  |  |

X
- Definition Aggregate offering price. + References No definition available. + Details
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Balance Type: | credit
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- Definition Percentage of underwriting discount on public offering price. + References No definition available. + Details
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- Definition Placement agent fee description. + References No definition available. + Details
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- Definition Shelf Registration statement amount. + References No definition available. + Details
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