Precentage of outstanding principle balance, description.

No definition available.

Name:	CLSN_PrecentageOfOutstandingPrincipleBalanceDescription
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Balance Type:	na
Period Type:	duration

- Definition

Warrant date.

+ References

No definition available.

+ Details

Name:	CLSN_WarrantDate
Namespace Prefix:	CLSN_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

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-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares.

+ References

No definition available.

+ Details

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

- Definition

The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

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

- Definition

The rate of interest that was being paid on the original debt issue that is being converted in the noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Name:	us-gaap_DebtConversionOriginalDebtInterestRateOfDebt
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

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+ Details

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

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Paragraph 1
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeVariableInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of the cost of borrowed funds accounted for as interest expense for debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
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-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
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-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

+ Details

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

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 14
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

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-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 15
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=CLSN_HorizonCreditAgreementMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=CLSN_HorizonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=CLSN_HerculesCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=CLSN_HerculesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=CLSN_EGENIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=CLSN_SecondTrancheMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=CLSN_LoanAgreementMember
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:	dei_LegalEntityAxis=CLSN_HerculesTechnologyGrowthCapitalIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Period Type:

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Note Payable (Details Narrative) - USD ($)					1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended	19 Months Ended	26 Months Ended
Note Payable (Details Narrative) - USD ($)	Jun. 27, 2018	Jun. 10, 2014	Jun. 10, 2014	Nov. 25, 2013	Jun. 20, 2014	Nov. 30, 2013	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 10, 2014	Dec. 15, 2016	Jun. 30, 2018	Dec. 17, 2015	Jun. 26, 2017
Class of warrant or right, exercise price of warrants or rights														$ 1.65
Hercules Warrant [Member]
Debt instrument, unamortized discount, total		$ 476,261	$ 476,261							$ 476,261
Horizon Credit Agreement [Member]
Precentage of outstanding principle balance, description									an amount equal to 1-3%
Interest expense, debt, total							$ 10,794		$ 10,794
Amortization of debt issuance costs							$ 4,237		$ 4,237
Horizon Credit Agreement [Member] \| Horizon Warrants [Member]
Class of warrant or right, number of securities called by each warrant or right							190,114		190,114			190,114
Class of warrant or right, exercise price of warrants or rights							$ 2.63		$ 2.63			$ 2.63
Debt instrument, unamortized discount, total							$ 507,116		$ 507,116			$ 507,116
Percentage for original debt, amount									4.00%
Debt issuance costs, gross							$ 400,000		$ 400,000			$ 400,000
Horizon Credit Agreement [Member] \| LIBOR plus [Member]
Line of credit, interest rate							7.625%		7.625%			7.625%
Horizon Credit Agreement [Member] \| Horizon [Member]
Debt instrument, unamortized discount, total							$ 100,000		$ 100,000			$ 100,000
Debt issuance costs, gross							782,116		782,116			782,116
Debt issuance costs, net, total							$ 175,000		175,000			$ 175,000
Hercules Credit Agreement [Member]
Interest expense, debt, total								$ 11,731	56,386
Amortization of debt issuance costs								$ 17,685	$ 35,370
Hercules Credit Agreement [Member] \| Hercules Warrant [Member]
Class of warrant or right, number of securities called by each warrant or right				6,963
Class of warrant or right, exercise price of warrants or rights				$ 50.26
Debt issuance costs, gross		$ 350,000	350,000							350,000
Warrant date				Nov. 25, 2018
Hercules Credit Agreement [Member] \| Prime Rate [Member]
Debt instrument, basis spread on variable rate											11.50%	11.75%	11.25%
Hercules Credit Agreement [Member] \| Hercules [Member]
Proceeds from lines of credit, total										$ 10,000,000
Debt instrument, unamortized discount, total						$ 230,000
Debt issuance costs, net, total						122,378
EGEN Inc [Member]
Payments to acquire businesses, gross					$ 3,000,000
EGEN Inc [Member] \| Hercules Credit Agreement [Member]
Payments to acquire businesses, gross			$ 3,000,000
Second Tranche [Member] \| Hercules Credit Agreement [Member]
Class of warrant or right, number of securities called by each warrant or right		6,963	6,963							6,963
Percentage for original debt, amount		3.50%
Original debt, amount		$ 5,000,000
Loan Agreement [Member] \| Horizon Technology Finance Corporation [Member]
Line of credit facility, maximum borrowing capacity	$ 10,000,000
Loan Agreement [Member] \| Hercules Technology Growth Capital, Inc. [Member]
Line of credit facility, maximum borrowing capacity						20,000,000
Horizon Credit Agreement [Member]
Proceeds from lines of credit, total	$ 10,000,000
Hercules Credit Agreement [Member] \| First Tranche [Member]
Proceeds from lines of credit, total						5,000,000
Repayments of lines of credit						$ 4,000,000
Hercules Credit Agreement [Member] \| Second Tranche [Member]
Proceeds from lines of credit, total			$ 5,000,000