Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Document and Entity Information
Document Type	10-Q
Document Period End Date	Jun. 30, 2020
Entity Registrant Name	Celldex Therapeutics, Inc.
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 Common Stock, Shares Outstanding		39,126,448
Entity Central Index Key	0000744218
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false