Organization and Plan of Business Operations	6 Months Ended
Jun. 30, 2017
Organization and Plan of Business Operations [Abstract]
Organization and Plan of Business Operations	Note 1 — Organization and Plan of Business Operations *Organization and General* NextDecade Corporation, formerly known as Harmony Merger Corp. (the “Company” or “Harmony”) was incorporated in Delaware on May 21, 2014 as a blank check company whose original objective was to acquire, through a merger, share exchange, asset acquisition, stock purchase, recapitalization, reorganization or other similar business combination, one or more businesses or entities (a “Business Combination”). All activity through June 30, 2017 relates to the Company’s formation, initial public offering and initial existence as Harmony and identifying suitable candidates for a Business Combination. On April 10, 2017, the Company formed Harmony Merger Sub, LLC as a wholly-owned subsidiary (“Merger Sub”), solely for effectuating a future business combination with NextDecade, LLC (“NextDecade”). Merger Sub was incorporated under the laws of Delaware. Merger Sub owns no material assets and does not operate any business. On April 17, 2017, the Company entered into an Agreement and Plan of Merger (the “Agreement”) by and among the Company, Harmony Merger Sub, LLC, a wholly-owned subsidiary of the Company (“Merger Sub”), NextDecade, York Credit Opportunities Investments Master Fund, L.P, York Multi-Strategy Master Fund, L.P., York Select Master Fund, L.P., York Global Finance 43, LLC, Valinor Management, L.P., Valinor Capital Partners SPV XXI, LLC, Halcyon Capital Management L.P., which, together with the Valinor Blocker Manager, are referred to as a “Blocker Manager” and, together, the “Blocker Managers”), Halcyon Energy, Power, and Infrastructure Capital Fund Offshore, LLC, Halcyon Energy, Power, and Infrastructure Capital Holdings Offshore LLC, and Halcyon Energy, Power, and Infrastructure Capital Fund LP. Pursuant to the Agreement, each of the Blocker Companies merged with and into the Company (each a “Blocker Merger” and, together, the “Blocker Mergers”), with the Company being the surviving entity of the Blocker Mergers and, immediately thereafter Merger Sub merged with and into NextDecade (the “Merger”) with NextDecade being the surviving entity of the Merger (the “Surviving Company”) and becoming a wholly-owned subsidiary of the Company. On July 24, 2017, subsequent to the end of the quarterly period to which this Quarterly Report on Form 10-Q relates, the Company completed its Business Combination by acquiring 100% of the outstanding membership interests in NextDecade (the “Closing”), see Note 8 – Subsequent Events. In connection with the completion of the Business Combination, on July 24, 2017, the Company changed its name from Harmony Merger Corp. to NextDecade Corporation and the Company’s common stock began trading on the Nasdaq Capital Market (“NASDAQ”) under the new ticker symbol “NEXT”. Unless otherwise specified herein, the information set forth in these notes to the Company’s condensed financial statements describes the Company and its operations as of and for the periods ended June 30, 2017 and 2016 and does not reflect the completion of the Business Combination. For further information, refer to the pro forma condensed consolidated combined financial statements in the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission (“SEC”) on July 28, 2017. *Financing* The registration statement for the Company’s initial public offering was declared effective on March 23, 2015. The Company consummated a public offering of 11,500,000 units (“Units”) on March 27, 2015 (the “Offering”), including the exercise of the over-allotment option (“Overallotment”) of 1,500,000 Units, generating gross proceeds of $115,000,000 and net proceeds of $112,605,665 after deducting $2,394,335 of transaction costs (up to an additional $4,325,000 of deferred underwriting expenses may be paid upon the completion of a business combination), which is discussed in Note 3. In addition, the Company generated gross and net proceeds of $5,585,000 from a private placement (the “Private Placement”) of units (“Private Units”) to certain of the Initial Stockholders (defined below) and Cantor Fitzgerald & Co., the representative of the underwriters in the Offering (“Cantor”), which is described in Note 4. *Trust Account* Following the closing of the Offering and the Private Placement on March 27, 2015, an amount of $117,300,000 (or $10.20 per share sold to the public in the Offering included in the Units (“Public Shares”)) from the sale of the Units and Private Units is being held in a trust account (“Trust Account”) and may be invested in money market funds meeting the applicable conditions of Rule 2a-7 promulgated under the Investment Company Act of 1940, as amended, and that invest solely in U.S. Treasuries or United States bonds, treasuries or notes having a maturity of 180 days or less. The $117,300,000 placed into the Trust Account may not be released until the earlier of (i) the consummation of the Company’s initial Business Combination and (ii) the Company’s failure to consummate a Business Combination within the prescribed time. The remaining net proceeds (not held in the Trust Account) may be used to pay for business, legal and accounting due diligence on prospective acquisitions and continuing general and administrative expenses. Additionally, the interest earned on the Trust Account balance may be released to the Company to pay the Company’s tax obligations. Placing funds in the Trust Account may not protect those funds from third party claims against the Company. Although the Company will seek to have all vendors, service providers, prospective target businesses or other entities it engages, execute agreements with the Company waiving any claim of any kind in or to any monies held in the Trust Account, there is no guarantee that such persons will execute such agreements. On March 27, 2017, the Company held an annual meeting of its stockholders (the “Meeting”). At the Meeting, the Company’s stockholders approved an amendment to the Company’s amended and restated certificate of incorporation (the “charter”) to extend the date that the Company must consummate a business combination (the “Extension”) to July 27, 2017 (the “Extended Date”). On March 27, 2017, the holders of 495,335 shares of the Company’s common stock exercised their right to convert their shares into cash at a conversion price of approximately $10.22 per share, for an aggregate conversion amount of $5,063,331. *Business Combination* The Company’s management had broad discretion with respect to the specific application of the net proceeds of the Offering and Private Placement, although substantially all of the net proceeds are intended to be generally applied toward consummating a Business Combination. The Company’s securities are listed on the Nasdaq Capital Market (“NASDAQ”). Pursuant to the NASDAQ listing rules, the Company’s initial Business Combination must be with a target business or businesses whose collective fair market value is at least equal to 80% of the balance in the trust account at the time of the execution of a definitive agreement for such Business Combination, although this may entail simultaneous acquisitions of several target businesses.

Note 1 — Organization and Plan of Business Operations

Organization and General

NextDecade Corporation, formerly known as Harmony Merger Corp. (the “Company” or “Harmony”) was incorporated in Delaware on May 21, 2014 as a blank check company whose original objective was to acquire, through a merger, share exchange, asset acquisition, stock purchase, recapitalization, reorganization or other similar business combination, one or more businesses or entities (a “Business Combination”).

All activity through June 30, 2017 relates to the Company’s formation, initial public offering and initial existence as Harmony and identifying suitable candidates for a Business Combination.

On April 10, 2017, the Company formed Harmony Merger Sub, LLC as a wholly-owned subsidiary (“Merger Sub”), solely for effectuating a future business combination with NextDecade, LLC (“NextDecade”). Merger Sub was incorporated under the laws of Delaware. Merger Sub owns no material assets and does not operate any business.

On April 17, 2017, the Company entered into an Agreement and Plan of Merger (the “Agreement”) by and among the Company, Harmony Merger Sub, LLC, a wholly-owned subsidiary of the Company (“Merger Sub”), NextDecade, York Credit Opportunities Investments Master Fund, L.P, York Multi-Strategy Master Fund, L.P., York Select Master Fund, L.P., York Global Finance 43, LLC, Valinor Management, L.P., Valinor Capital Partners SPV XXI, LLC, Halcyon Capital Management L.P., which, together with the Valinor Blocker Manager, are referred to as a “Blocker Manager” and, together, the “Blocker Managers”), Halcyon Energy, Power, and Infrastructure Capital Fund Offshore, LLC, Halcyon Energy, Power, and Infrastructure Capital Holdings Offshore LLC, and Halcyon Energy, Power, and Infrastructure Capital Fund LP. Pursuant to the Agreement, each of the Blocker Companies merged with and into the Company (each a “Blocker Merger” and, together, the “Blocker Mergers”), with the Company being the surviving entity of the Blocker Mergers and, immediately thereafter Merger Sub merged with and into NextDecade (the “Merger”) with NextDecade being the surviving entity of the Merger (the “Surviving Company”) and becoming a wholly-owned subsidiary of the Company.

On July 24, 2017, subsequent to the end of the quarterly period to which this Quarterly Report on Form 10-Q relates, the Company completed its Business Combination by acquiring 100% of the outstanding membership interests in NextDecade (the “Closing”), see Note 8 – Subsequent Events. In connection with the completion of the Business Combination, on July 24, 2017, the Company changed its name from Harmony Merger Corp. to NextDecade Corporation and the Company’s common stock began trading on the Nasdaq Capital Market (“NASDAQ”) under the new ticker symbol “NEXT”. Unless otherwise specified herein, the information set forth in these notes to the Company’s condensed financial statements describes the Company and its operations as of and for the periods ended June 30, 2017 and 2016 and does not reflect the completion of the Business Combination. For further information, refer to the pro forma condensed consolidated combined financial statements in the Company’s Current Report on Form 8-K filed with the Securities and Exchange Commission (“SEC”) on July 28, 2017.

Financing

The registration statement for the Company’s initial public offering was declared effective on March 23, 2015. The Company consummated a public offering of 11,500,000 units (“Units”) on March 27, 2015 (the “Offering”), including the exercise of the over-allotment option (“Overallotment”) of 1,500,000 Units, generating gross proceeds of $115,000,000 and net proceeds of $112,605,665 after deducting $2,394,335 of transaction costs (up to an additional $4,325,000 of deferred underwriting expenses may be paid upon the completion of a business combination), which is discussed in Note 3. In addition, the Company generated gross and net proceeds of $5,585,000 from a private placement (the “Private Placement”) of units (“Private Units”) to certain of the Initial Stockholders (defined below) and Cantor Fitzgerald & Co., the representative of the underwriters in the Offering (“Cantor”), which is described in Note 4.

Trust Account

Following the closing of the Offering and the Private Placement on March 27, 2015, an amount of $117,300,000 (or $10.20 per share sold to the public in the Offering included in the Units (“Public Shares”)) from the sale of the Units and Private Units is being held in a trust account (“Trust Account”) and may be invested in money market funds meeting the applicable conditions of Rule 2a-7 promulgated under the Investment Company Act of 1940, as amended, and that invest solely in U.S. Treasuries or United States bonds, treasuries or notes having a maturity of 180 days or less. The $117,300,000 placed into the Trust Account may not be released until the earlier of (i) the consummation of the Company’s initial Business Combination and (ii) the Company’s failure to consummate a Business Combination within the prescribed time. The remaining net proceeds (not held in the Trust Account) may be used to pay for business, legal and accounting due diligence on prospective acquisitions and continuing general and administrative expenses. Additionally, the interest earned on the Trust Account balance may be released to the Company to pay the Company’s tax obligations. Placing funds in the Trust Account may not protect those funds from third party claims against the Company. Although the Company will seek to have all vendors, service providers, prospective target businesses or other entities it engages, execute agreements with the Company waiving any claim of any kind in or to any monies held in the Trust Account, there is no guarantee that such persons will execute such agreements.

On March 27, 2017, the Company held an annual meeting of its stockholders (the “Meeting”). At the Meeting, the Company’s stockholders approved an amendment to the Company’s amended and restated certificate of incorporation (the “charter”) to extend the date that the Company must consummate a business combination (the “Extension”) to July 27, 2017 (the “Extended Date”). On March 27, 2017, the holders of 495,335 shares of the Company’s common stock exercised their right to convert their shares into cash at a conversion price of approximately $10.22 per share, for an aggregate conversion amount of $5,063,331.

Business Combination

The Company’s management had broad discretion with respect to the specific application of the net proceeds of the Offering and Private Placement, although substantially all of the net proceeds are intended to be generally applied toward consummating a Business Combination. The Company’s securities are listed on the Nasdaq Capital Market (“NASDAQ”). Pursuant to the NASDAQ listing rules, the Company’s initial Business Combination must be with a target business or businesses whose collective fair market value is at least equal to 80% of the balance in the trust account at the time of the execution of a definitive agreement for such Business Combination, although this may entail simultaneous acquisitions of several target businesses.