Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	NextDecade Corp.
Entity Central Index Key	0001612720
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Common Stock Outstanding		109,979,473
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1