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v3.20.1

Earn-out Milestone Liability (Details Narrative) - USD ($) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Gain (loss) from change in fair value of earn out milestone liability | $ (41,274) |  |  |
Fair Value Earnout Milestone Liability [Member] |  |  |  |
Earnout milestone liability | 5,800,000 | $ 5,800,000 | $ 5,700,000 | $ 8,900,000
Gain on non-cash benefit | $ 100,000 | $ 3,100,000 |  |
Fair Value Earnout Milestone Liability [Member] | Payment Option One [Member] |  |  |  |
Risk adjusted assessment of each milestone | 80.00% | 80.00% |  |
Fair Value Earnout Milestone Liability [Member] | Payment Option Two [Member] |  |  |  |
Risk adjusted assessment of each milestone | 20.00% | 20.00% |  |
Amended Asset Purchase Agreement Option Payment 1 [Member] |  |  |  |
Gain (loss) from change in fair value of earn out milestone liability | $ 7,000,000 | $ 7,000,000 |  |
Amended Asset Purchase Agreement Option Payment 2 [Member] |  |  |  |
Gain (loss) from change in fair value of earn out milestone liability | $ 12,400,000 | $ 12,400,000 |  |

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- Definition Earnout milestone liability. + References No definition available. + Details
Name: | CLSN_EarnoutMilestoneLiability1
Namespace Prefix: | CLSN_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of gain (loss) from the change in the fair value of earn-out milestone liability. + References No definition available. + Details
Name: | CLSN_GainLossFromChangeInFairValueOfEarnOutMilestoneLiability
Namespace Prefix: | CLSN_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Gain on non-cash benefit. + References No definition available. + Details
Name: | CLSN_GainOnNoncashBenefit
Namespace Prefix: | CLSN_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The percentage of risk-adjusted assessment of each milestone. + References No definition available. + Details
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Namespace Prefix: | CLSN_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
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