Earnout milestone liability.

No definition available.

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Namespace Prefix:	CLSN_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Earn-out payment options, description.

+ References

No definition available.

+ Details

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Namespace Prefix:	CLSN_
Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Non-cash charge on earnout milestone liability.

+ References

No definition available.

+ Details

Name:	CLSN_NoncashChargeOnEarnoutMilestoneLiability
Namespace Prefix:	CLSN_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6405-128476

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Exercise price per share or per unit of warrants or rights outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21475-112644

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of warrants or rights which entitle the entity to receive future services in exchange for the unvested, forfeitable warrants or rights.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 50
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6784392&loc=d3e188667-122775

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=CLSN_CertainBusinessDaysOfAchievingMilestoneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=CLSN_FairValueEarnoutMilestoneLiabilityMember
Namespace Prefix:
Data Type:	na
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Period Type:

EARN-OUT MILESTONE LIABILITY (Details Narrative) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Jun. 20, 2014	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 31, 2020	Feb. 28, 2020	Mar. 28, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Warrants to purchase common stock		7,273				213,333
Warrant price per share		$ 48.30
EGWC, Inc [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Earnout payment options description	each milestone (10% to 67%) and utilizing a discount rate based on the estimated time to achieve the milestone (1.5 to 2.5 years).
Non-cash charge on earnout milestone liability		$ 1.6	$ 1.3	$ 5.7
Amended Asset Purchase Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Earnout milestone liability	$ 13.9						$ 12.4
Warrants to purchase common stock					13,333		13,333
Warrant price per share		$ 30.00					$ 0.15
Right to receiving warrant					13,151
Amended Asset Purchase Agreement [Member] \| Within One Year of Achieving Milestone [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Earnout milestone liability	$ 30.4						$ 12.4
Amended Asset Purchase Agreement [Member] \| 10 Business Days of Achieving Milestone [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Earnout milestone liability							$ 7.0
Fair Value Earnout Milestone Liability [Member] \| EGWC, Inc [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Business Combination, Consideration Transferred, Liabilities Incurred		$ 5.4	$ 7.0