The amount of estimated time to achieve the milestone.

No definition available.

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Namespace Prefix:	clsn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of gain (loss) from the change in the fair value of earn-out milestone liability.

+ References

No definition available.

+ Details

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Namespace Prefix:	clsn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The percentage of risk-adjusted assessment of each milestone.

+ References

No definition available.

+ Details

Name:	clsn_RiskAdjustedAssessmentOfEachMilestone
Namespace Prefix:	clsn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

+ Details

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

- Definition

For contingent consideration arrangements recognized in connection with a business combination, this element represents an estimate of the high-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_BusinessAcquisitionAxis=clsn_EGENIncMember
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Note 11 - Earn-out Milestone Liability (Details Textual) - USD ($)	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 20, 2014	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Gain (Loss) from Change in Fair Value of Earn out Milestone Liability						$ 575,979
Minimum [Member]
Risk Adjusted Assessment of Each Milestone		50.00%	50.00%	10.00%	10.00%	50.00%	10.00%	50.00%	10.00%
Estimated Time to Achieve the Milestone		1 year 182 days	1 year 273 days	182 days	91 days			2 years	182 days
Maximum [Member]
Risk Adjusted Assessment of Each Milestone		80.00%	80.00%	75.00%	75.00%	80.00%	75.00%	80.00%	75.00%
Estimated Time to Achieve the Milestone		2 years	2 years 91 days	2 years	2 years 91 days			2 years 182 days	2 years 182 days
EGEN Inc [Member]
Gain (Loss) from Change in Fair Value of Earn out Milestone Liability		$ 292,228		$ 408,684		$ 575,979	$ 106,028
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	$ 30,400,000
Business Combination, Consideration Transferred, Liabilities Incurred	$ 13,900,000		$ 13,500,000		$ 14,200,000	$ 13,800,000	$ 13,800,000	$ 13,200,000	$ 13,900,000
EGEN Inc [Member] \| Minimum [Member]
Risk Adjusted Assessment of Each Milestone	10.00%
Estimated Time to Achieve the Milestone	1 year 182 days
EGEN Inc [Member] \| Maximum [Member]
Risk Adjusted Assessment of Each Milestone	67.00%
Estimated Time to Achieve the Milestone	2 years 182 days