Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 13, 2020	Jun. 30, 2019
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	Celldex Therapeutics, Inc.
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 40
Entity Common Stock, Shares Outstanding		17,574,679
Entity Central Index Key	0000744218
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false