Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net loss (income) attributable to NextDecade Corporation	$ (3,658)	$ 902
Adjustment to reconcile net loss (income) to net cash used in operating activities
Depreciation	48	16
Share-based compensation expense (forfeiture)	(3,729)	(1,860)
Loss (gain) on common stock warrant liabilities	2,038	(8,339)
Realized loss on investment securities	0	423
Amortization of right-of-use assets	139	324
Amortization of other non-current assets	354	177
Changes in operating assets and liabilities:
Prepaid expenses	(169)	(218)
Accounts payable	(45)	(28)
Operating lease liabilities	(158)	(271)
Accrued expenses and other liabilities	1,390	(5,364)
Net cash used in operating activities	(3,790)	(14,238)
Investing activities:
Acquisition of property, plant and equipment	(2,384)	(13,826)
Acquisition of other non-current assets	(1,533)	(6,107)
Proceeds from sale of investment securities	0	61,972
Purchase of investment securities	0	(188)
Net cash (used in) provided by investing activities	(3,917)	41,851
Financing activities:
Proceeds from sale of Rio Bravo	0	15,000
Proceeds from equity issuance	24,500	0
Preferred stock dividends	(13)	(13)
Equity issuance costs	(54)	0
Shares repurchased related to share-based compensation	(44)	(57)
Net cash provided by financing activities	24,389	14,930
Net increase in cash and cash equivalents	16,682	42,543
Cash and cash equivalents – beginning of period	22,608	15,736
Cash and cash equivalents – end of period	39,290	58,279
Non-cash investing activities:
Accounts payable for acquisition of property, plant and equipment	79	3,341
Accrued liabilities for acquisition of property, plant and equipment	395	7,862
Pipeline assets obtained in exchange for other non-current liabilities	84	0
Non-cash financing activities:
Paid-in-kind dividends on Series A and Series B Convertible Preferred Stock	3,862	3,430
Accretion of deemed dividends on Series A Convertible Preferred Stock	$ 16	$ 76