Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 03, 2021
Cover Abstract
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-38905
Entity Registrant Name	NextCure, Inc.
Entity Central Index Key	0001661059
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-5231247
Entity Address, Address Line One	9000 Virginia Manor Road
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Beltsville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20705
City Area Code	240
Local Phone Number	399-4900
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	NXTC
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		27,626,227
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false