Nature of Business	6 Months Ended
Jun. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business Syndax Pharmaceuticals, Inc. (the Company) is a clinical stage biopharmaceutical company developing an innovative pipeline of combination therapies in multiple cancer indications. The Company’s lead product candidate, entinostat, is currently being evaluated in a Phase 3 clinical trial for advanced hormone receptor positive, human epidermal growth factor receptor 2 negative breast cancer. The U.S. Food and Drug Administration granted Breakthrough Therapy designation to entinostat when given in combination with exemestane following positive results from the Company’s ENCORE 301 Phase 2b clinical trial. Given its potential ability to block the function of immune suppressive cells in the tumor microenvironment, the Company is evaluating entinostat as a combination therapeutic in Phase 1b/2 clinical trials with Merck & Co., Inc. for non-small cell lung cancer, melanoma and microsatellite stable colorectal cancer; with Genentech, Inc. for triple negative breast cancer; and with Merck KGaA, Darmstadt, Germany, and Pfizer Inc. for ovarian cancer. The Company’s second product candidate, SNDX-6352, is a monoclonal antibody that targets the colony stimulating factor-1 receptor to enhance the body’s immune response against tumors that have shown sensitivity to immunotherapy. The Company is evaluating SNDX-6352 in a Phase 1 clinical trial. The Company plans to continue to leverage the technical and business expertise of our management team and scientific collaborators to license, acquire and develop additional cancer therapies to expand our pipeline. In March 2016, the Company completed its initial public offering (“IPO”) whereby it sold 4,809,475 shares of common stock at the initial public offering price of $12.00 per share, which included 409,475 shares issued pursuant to the underwriters’ partial exercise of their over-allotment option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were $50.5 million, net of underwriting discounts and commissions of $4.0 million and offering expenses of $3.1 million. Upon the closing of the IPO, all outstanding shares of the Company’s outstanding convertible preferred stock converted into 12,872,551 shares of common stock; and the Company’s outstanding warrant liability to purchase 357,840 shares of the Company’s common stock valued at $4.6 million was reclassified to additional paid-in capital. In connection with the closing of the Company’s IPO, the Company filed an amended and restated certificate of incorporation and adopted amended and restated bylaws, both of which were approved by the Company’s board of directors and stockholders on September 28, 2015 and February 24, 2016, respectively. Pursuant to the amended and restated certificate of incorporation, the Company is now authorized to issue 100,000,000 shares of common stock and 10,000,000 shares of preferred stock. In May 2017, the Company completed a follow-on public offering whereby the Company sold 3,950,190 shares of common stock at a price of $13.25 per share, which included 200,190 shares issued pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were approximately $48.7 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. Since its inception, the Company has devoted its efforts principally to research and development and raising capital. The Company is subject to risks common to companies in the development stage, including, but not limited to, successful development of therapeutics, obtaining additional funding, protection of proprietary therapeutics, compliance with government regulations, fluctuations in operating results, dependence on key personnel and collaborative partners, and risks associated with industry changes. The Company’s long-term success is dependent upon its ability to successfully develop and market its product candidates, expand its oncology drug pipeline, earn revenue, obtain additional capital when needed, and ultimately, achieve profitable operations. The Company anticipates that it will be two or more years before either entinostat or SNDX-6352 is approved, if ever, and the Company begins to generate revenue from sales of either entinostat or SNDX-6352. Accordingly, management expects to incur substantial losses on the ongoing development of entinostat and SNDX-6352 and does not expect to achieve positive cash flow from operations for the foreseeable future, if ever. As a result, the Company will continue to require additional capital to move forward with its business plan. While certain amounts of this additional capital were raised in the past, there can be no assurance that funds necessary beyond these amounts will be available in amounts or on terms sufficient to ensure ongoing operations. The Company’s management believes that the cash, cash equivalents and short-term investments balances as of June 30, 2017 should enable the Company to maintain its planned operations for at least the next 12 months. The Company’s ability to fund all of its planned operations internally beyond that date, including the completion of its ongoing and planned clinical trial activities, may be substantially dependent upon whether the Company can obtain sufficient funding on terms acceptable to the Company. Proceeds from additional capital transactions would allow the Company to accelerate and/or expand its planned research and development activities. In the event that sufficient funds are not available, the Company may be required to delay or reduce expenditures to conserve cash, which could involve scaling back or curtailing development and general and administrative activities.

1. Nature of Business

Syndax Pharmaceuticals, Inc. (the Company) is a clinical stage biopharmaceutical company developing an innovative pipeline of combination therapies in multiple cancer indications. The Company’s lead product candidate, entinostat, is currently being evaluated in a Phase 3 clinical trial for advanced hormone receptor positive, human epidermal growth factor receptor 2 negative breast cancer. The U.S. Food and Drug Administration granted Breakthrough Therapy designation to entinostat when given in combination with exemestane following positive results from the Company’s ENCORE 301 Phase 2b clinical trial. Given its potential ability to block the function of immune suppressive cells in the tumor microenvironment, the Company is evaluating entinostat as a combination therapeutic in Phase 1b/2 clinical trials with Merck & Co., Inc. for non-small cell lung cancer, melanoma and microsatellite stable colorectal cancer; with Genentech, Inc. for triple negative breast cancer; and with Merck KGaA, Darmstadt, Germany, and Pfizer Inc. for ovarian cancer. The Company’s second product candidate, SNDX-6352, is a monoclonal antibody that targets the colony stimulating factor-1 receptor to enhance the body’s immune response against tumors that have shown sensitivity to immunotherapy. The Company is evaluating SNDX-6352 in a Phase 1 clinical trial. The Company plans to continue to leverage the technical and business expertise of our management team and scientific collaborators to license, acquire and develop additional cancer therapies to expand our pipeline.

In March 2016, the Company completed its initial public offering (“IPO”) whereby it sold 4,809,475 shares of common stock at the initial public offering price of $12.00 per share, which included 409,475 shares issued pursuant to the underwriters’ partial exercise of their over-allotment option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were $50.5 million, net of underwriting discounts and commissions of $4.0 million and offering expenses of $3.1 million. Upon the closing of the IPO, all outstanding shares of the Company’s outstanding convertible preferred stock converted into 12,872,551 shares of common stock; and the Company’s outstanding warrant liability to purchase 357,840 shares of the Company’s common stock valued at $4.6 million was reclassified to additional paid-in capital. In connection with the closing of the Company’s IPO, the Company filed an amended and restated certificate of incorporation and adopted amended and restated bylaws, both of which were approved by the Company’s board of directors and stockholders on September 28, 2015 and February 24, 2016, respectively. Pursuant to the amended and restated certificate of incorporation, the Company is now authorized to issue 100,000,000 shares of common stock and 10,000,000 shares of preferred stock.

In May 2017, the Company completed a follow-on public offering whereby the Company sold 3,950,190 shares of common stock at a price of $13.25 per share, which included 200,190 shares issued pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock. The aggregate net proceeds received by the Company from the offering were approximately $48.7 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company.

Since its inception, the Company has devoted its efforts principally to research and development and raising capital. The Company is subject to risks common to companies in the development stage, including, but not limited to, successful development of therapeutics, obtaining additional funding, protection of proprietary therapeutics, compliance with government regulations, fluctuations in operating results, dependence on key personnel and collaborative partners, and risks associated with industry changes. The Company’s long-term success is dependent upon its ability to successfully develop and market its product candidates, expand its oncology drug pipeline, earn revenue, obtain additional capital when needed, and ultimately, achieve profitable operations. The Company anticipates that it will be two or more years before either entinostat or SNDX-6352 is approved, if ever, and the Company begins to generate revenue from sales of either entinostat or SNDX-6352. Accordingly, management expects to incur substantial losses on the ongoing development of entinostat and SNDX-6352 and does not expect to achieve positive cash flow from operations for the foreseeable future, if ever. As a result, the Company will continue to require additional capital to move forward with its business plan. While certain amounts of this additional capital were raised in the past, there can be no assurance that funds necessary beyond these amounts will be available in amounts or on terms sufficient to ensure ongoing operations.

The Company’s management believes that the cash, cash equivalents and short-term investments balances as of June 30, 2017 should enable the Company to maintain its planned operations for at least the next 12 months. The Company’s ability to fund all of its planned operations internally beyond that date, including the completion of its ongoing and planned clinical trial activities, may be substantially dependent upon whether the Company can obtain sufficient funding on terms acceptable to the Company. Proceeds from additional capital transactions would allow the Company to accelerate and/or expand its planned research and development activities. In the event that sufficient funds are not available, the Company may be required to delay or reduce expenditures to conserve cash, which could involve scaling back or curtailing development and general and administrative activities.