Represents the term of the collaborative arrangement.

No definition available.

Name:	cldx_CollaborativeArrangementAgreementTerm
Namespace Prefix:	cldx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents percentage of reimbursement of external costs incurred by the company.

+ References

No definition available.

+ Details

Name:	cldx_ReimbursementOfExternalCostsIncurredPercentage
Namespace Prefix:	cldx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents revenue earned during the period arising from products sold or services provided under the terms of a contract. Also include revenue earned during the period from non-repayable sum of money awarded to an entity to carry out a specific purpose as provided in grant agreements.

+ References

No definition available.

+ Details

Name:	cldx_RevenueFromContractsAndGrants
Namespace Prefix:	cldx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents revenue from product development and licensing agreements.

+ References

No definition available.

+ Details

Name:	cldx_RevenueFromProductDevelopmentAndLicensingAgreements
Namespace Prefix:	cldx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response)
-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 13
-Section A

+ Details

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

- Details

Name:	us-gaap_CounterpartyNameAxis=cldx_BristolMeyersSquibbCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=cldx_Pd1ImmuneCheckpointInhibitorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=cldx_RockefellerUniversityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Revenue (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
Revenue (Details) - USD ($) $ in Thousands	May 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
REVENUE
Deferred Revenue		$ 4,172		$ 4,172		$ 4,368
Product development and licensing agreements revenue		604	$ 334	1,057	$ 676
Contracts and grants revenue		785	1,844	1,635	1,988
BMS \| PD-1 Immune Checkpoint Inhibitor
REVENUE
Term of the agreement	5 years
Deferred Revenue	$ 5,000
Reimbursement of external costs incurred by the company (as a percent)	50.00%
Product development and licensing agreements revenue		600	300	1,000	600
Rockefeller
REVENUE
Contracts and grants revenue		$ 400	$ 1,500	$ 800	$ 1,600