Note 13 - Earn-out Milestone Liability - Summary of the Changes in the Earn-out Milestone Liability (Details)	3 Months Ended
Mar. 31, 2017 USD ($)
Balance	$ 13,188,226
Non-cash charge from the adjustment for the change in fair value included in net loss	283,751
Balance	$ 13,471,977

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

No definition available.

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