| Document And Entity Information | Mar. 18, 2021 |
| Document Information [Line Items] | |
| Entity, Registrant Name | NEXTDECADE CORPORATION |
| Document, Type | 8-K |
| Document, Period End Date | Mar. 18, 2021 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 001-36842 |
| Entity, Tax Identification Number | 46-5723951 |
| Entity, Address, Address Line One | 1000 Louisiana Street |
| Entity, Address, City or Town | Houston |
| Entity, Address, State or Province | TX |
| Entity, Address, Postal Zip Code | 77002 |
| City Area Code | 713 |
| Local Phone Number | 574-1880 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | NEXT |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001612720 |
