Consolidated Statements of Stockholders' Equity, Series A and Series B Convertible Preferred Stock - USD ($) shares in Thousands, $ in Thousands	Series A Preferred Stock [Member] Common Stock [Member]	Series A Preferred Stock [Member] Treasury Stock [Member]	Series A Preferred Stock [Member] Additional Paid-in Capital [Member]	Series A Preferred Stock [Member] Retained Earnings [Member]	Series A Preferred Stock [Member] AOCI Attributable to Parent [Member]	Series A Preferred Stock [Member] Series A Convertible Preferred Stock [Member]	Series A Preferred Stock [Member] Series B Convertible Preferred Stock [Member]	Series A Preferred Stock [Member]	Series B Preferred Stock [Member] Common Stock [Member]	Series B Preferred Stock [Member] Treasury Stock [Member]	Series B Preferred Stock [Member] Additional Paid-in Capital [Member]	Series B Preferred Stock [Member] Retained Earnings [Member]	Series B Preferred Stock [Member] AOCI Attributable to Parent [Member]	Series B Preferred Stock [Member] Series A Convertible Preferred Stock [Member]	Series B Preferred Stock [Member] Series B Convertible Preferred Stock [Member]	Series B Preferred Stock [Member]	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Total
Balance (in shares) at Dec. 31, 2017																	106,275
Balance at Dec. 31, 2017																	$ 11		$ 158,738	$ (55,617)	$ (40)			$ 103,092
Adoption of new accounting policy (Accounting Standards Update 2016-01 [Member]) at Dec. 31, 2017																				(40)	40
Share-based compensation																			19,032					19,032
Restricted stock vesting (in shares)																	173
Restricted stock vesting
Shares repurchased related to share-based compensation (in shares)																	(6)	6
Shares repurchased related to share-based compensation																		$ (35)						(35)
Issuance of stock (in shares)	414
Issuance of stock			$ 4,638			$ 38,549		$ 4,638							$ 26,159
Preferred stock dividends																			(724)			720		(724)
Deemed dividends - accretion of beneficial conversion feature																			(822)			822		(822)
Net loss attributable to NextDecade Corporation																				(41,960)				(41,960)
Balance (in shares) at Dec. 31, 2018																	106,856	6
Balance at Dec. 31, 2018																	$ 11	$ (35)	180,862	(97,617)		40,091	26,159	83,221
Adoption of new accounting policy (Accounting Standards Update 2016-02 [Member]) at Dec. 31, 2018																				(213)				(213)
Adoption of new accounting policy (Accounting Standards Update 2018-07 [Member]) at Dec. 31, 2018																			2,116					2,116
Share-based compensation																			(8,525)					(8,525)
Restricted stock vesting (in shares)																	510
Restricted stock vesting																			495					495
Shares repurchased related to share-based compensation (in shares)																	(131)	131
Shares repurchased related to share-based compensation																		$ (650)						(650)
Issuance of stock (in shares)																	10,094
Issuance of stock															$ 19,009		$ 1		61,824					61,825
Preferred stock dividends																			(11,164)			6,476	4,646	(11,164)
Deemed dividends - accretion of beneficial conversion feature																			(1,517)			1,517		(1,517)
Net loss attributable to NextDecade Corporation																				(35,871)				(35,871)
Balance (in shares) at Dec. 31, 2019																	117,329	137
Balance at Dec. 31, 2019																	$ 12	$ (685)	$ 224,091	$ (133,701)		$ 48,084	$ 49,814	$ 89,717