It represents the additional sale of common stock maximum amount.

No definition available.

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

- Definition

Represents the common stock available for sale.

+ References

No definition available.

+ Details

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

- Definition

Amount remaining of stock issued authorized.

+ References

No definition available.

+ Details

Name:	cldx_StockIssuedRemainingAuthorizedAmount
Namespace Prefix:	cldx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585

+ Details

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

- Definition

Number of shares of stock issued attributable to transactions classified as other.

+ References

No definition available.

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesOther
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
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_SubsidiarySaleOfStockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
Stockholders' Equity (Details) - USD ($) $ in Thousands	Nov. 30, 2017	May 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Common Stock
Aggregate offering price stock sale		$ 60,000
Additional offering price stock sale authorized	$ 75,000
Net proceeds from sale of common stock			$ 11,689	$ 12,821
Common Stock
Common Stock
Shares Issued in Connection with Cantor Agreement (in shares)			4,692,024
Aggregate gross offering price available			$ 55,500