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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) unrealized gain less than 12 months.

No definition available.

Name:	CLSN_DebtSecuritiesAvailableforsaleContinuousUnrealizedGainPositionLessThan12Months
Namespace Prefix:	CLSN_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of accumulated unrealized gain on investment in debt security measured at fair value with change in other comprehensive income (available-for-sale), unrealized gain for less than 12 months.

No definition available.

Name:	CLSN_DebtSecuritiesAvailableforsaleContinuousUnrealizedGainPositionLessThan12MonthsAccumulatedGain
Namespace Prefix:	CLSN_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- References

No definition available.