Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net loss attributable to NextDecade Corporation	$ (14,016)	$ (12,050)
Adjustment to reconcile net loss to net cash used in operating activities
Depreciation	136	146
Share-based compensation expense (forfeiture)	(5,571)	(759)
Loss (gain) on common stock warrant liabilities	2,363	(6,147)
Realized loss on investment securities	0	423
Amortization of right-of-use assets	414	984
Amortization of other non-current assets	1,062	1,042
Changes in operating assets and liabilities:
Prepaid expenses	(234)	61
Accounts payable	76	(478)
Operating lease liabilities	(396)	(710)
Accrued expenses and other liabilities	3,914	(5,258)
Net cash used in operating activities	(12,252)	(22,746)
Investing activities:
Acquisition of property, plant and equipment	(8,390)	(30,088)
Acquisition of other non-current assets	(4,666)	(9,390)
Proceeds from sale of investment securities	0	61,972
Purchase of investment securities	0	(188)
Net cash (used in) provided by investing activities	(13,056)	22,306
Financing activities:
Proceeds from sale of Rio Bravo	0	15,000
Proceeds from sale of Series C Convertible Preferred Stock	39,500	0
Proceeds from sale of common stock	389	0
Equity issuance costs	(117)	0
Preferred stock dividends	(50)	(41)
Shares repurchased related to share-based compensation	(279)	(322)
Net cash provided by financing activities	39,443	14,637
Net increase in cash and cash equivalents	14,135	14,197
Cash and cash equivalents – beginning of period	22,608	15,736
Cash and cash equivalents – end of period	36,743	29,933
Non-cash investing activities:
Accounts payable for acquisition of property, plant and equipment	329	479
Accrued liabilities for acquisition of property, plant and equipment	996	382
Pipeline assets obtained in exchange for other non-current liabilities	84	6,670
Non-cash financing activities:
Paid-in-kind dividends on Convertible Preferred Stock	12,965	10,524
Accretion of deemed dividends on Series A Convertible Preferred Stock	47	113
Accounts payable for equity issuance costs	148	0
Accrued liabilities for equity issuance costs	$ 35	$ 0