Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 13, 2020
Document Information [Line Items]
Entity Registrant Name	NextDecade Corp.
Entity Central Index Key	0001612720
Trading Symbol	next
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding (in shares)		120,623,534
Entity Shell Company	false
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Title of 12(b) Security	Common Stock, $0.0001 par value