Nature of Operations	3 Months Ended
Mar. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Operations	1. Nature of Operations Sage Therapeutics, Inc. (“Sage” or the “Company”) is a clinical-stage biopharmaceutical company committed to developing and commercializing novel medicines to treat life-altering central nervous system, or CNS, disorders, where there are no approved therapies or existing therapies are inadequate. The Company has a portfolio of product candidates with a current focus on modulating two critical CNS receptor systems, GABA and NMDA. The GABA receptor family, which is recognized as the major inhibitory neurotransmitter in the CNS, mediates downstream neurologic and bodily function via activation of GABA_A receptors. The NMDA-type receptors of the glutamate receptor system are a major excitatory receptor system in the CNS. Dysfunction in these systems is implicated in a broad range of CNS disorders. The Company is targeting CNS indications where patient populations are easily identified, clinical endpoints are well-defined, and development pathways are feasible. The Company was incorporated under the laws of the State of Delaware on April 16, 2010, and commenced operations on January 19, 2011 as Sterogen Biopharma, Inc. On September 13, 2011, the Company changed its name to Sage Therapeutics, Inc. under its Second Amended and Restated Certificate of Incorporation. The Company is subject to risks and uncertainties common to companies in the biotech industry, including, but not limited to, the risks associated with developing product candidates at each stage of non-clinical and clinical development; the challenges associated with gaining regulatory approval of such product candidates; the risks associated with commercializing pharmaceutical products, if it is able to obtain regulatory approval; the potential for development by third parties of new technological innovations that may compete with the Company’s products; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; and the uncertainty of being able to secure additional capital when needed to fund operations. The Company has incurred losses and negative cash flows from operations since its inception. As of March 31, 2017, the Company had an accumulated deficit of $377.1 million. From its inception through March 31, 2017, the Company received net proceeds of $643.3 million from the sales of redeemable convertible preferred stock, the issuance of convertible notes, and the proceeds from its initial public offering (“IPO”) in July 2014 and follow-on underwritten public offerings in April 2015, January 2016 and September 2016. Until such time, if ever, as the Company can generate substantial product revenue, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other sources of funding. If the Company is unable to raise additional funds through equity or debt financings when needed, the Company may be required to delay, limit, reduce or terminate product development or future commercialization efforts or grant rights to develop and market products or product candidates that the Company would otherwise prefer to develop and market itself. Based on its current operating plans, the Company believes its cash, cash equivalents and marketable securities of $342.6 million as of March 31, 2017 will be sufficient to fund its anticipated level of operations and capital expenditures into the second quarter of 2018. In August 2014, the Financial Accounting Standards Board issued Accounting Standards Update, or ASU, 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. After performing this evaluation, the Company believes that it has adequate cash resources to operate for 12 months from the date of issuance of these financial statements.

1. Nature of Operations

Sage Therapeutics, Inc. (“Sage” or the “Company”) is a clinical-stage biopharmaceutical company committed to developing and commercializing novel medicines to treat life-altering central nervous system, or CNS, disorders, where there are no approved therapies or existing therapies are inadequate. The Company has a portfolio of product candidates with a current focus on modulating two critical CNS receptor systems, GABA and NMDA. The GABA receptor family, which is recognized as the major inhibitory neurotransmitter in the CNS, mediates downstream neurologic and bodily function via activation of GABA_A receptors. The NMDA-type receptors of the glutamate receptor system are a major excitatory receptor system in the CNS. Dysfunction in these systems is implicated in a broad range of CNS disorders. The Company is targeting CNS indications where patient populations are easily identified, clinical endpoints are well-defined, and development pathways are feasible.

The Company was incorporated under the laws of the State of Delaware on April 16, 2010, and commenced operations on January 19, 2011 as Sterogen Biopharma, Inc. On September 13, 2011, the Company changed its name to Sage Therapeutics, Inc. under its Second Amended and Restated Certificate of Incorporation.

The Company is subject to risks and uncertainties common to companies in the biotech industry, including, but not limited to, the risks associated with developing product candidates at each stage of non-clinical and clinical development; the challenges associated with gaining regulatory approval of such product candidates; the risks associated with commercializing pharmaceutical products, if it is able to obtain regulatory approval; the potential for development by third parties of new technological innovations that may compete with the Company’s products; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; and the uncertainty of being able to secure additional capital when needed to fund operations.

The Company has incurred losses and negative cash flows from operations since its inception. As of March 31, 2017, the Company had an accumulated deficit of $377.1 million. From its inception through March 31, 2017, the Company received net proceeds of $643.3 million from the sales of redeemable convertible preferred stock, the issuance of convertible notes, and the proceeds from its initial public offering (“IPO”) in July 2014 and follow-on underwritten public offerings in April 2015, January 2016 and September 2016. Until such time, if ever, as the Company can generate substantial product revenue, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other sources of funding. If the Company is unable to raise additional funds through equity or debt financings when needed, the Company may be required to delay, limit, reduce or terminate product development or future commercialization efforts or grant rights to develop and market products or product candidates that the Company would otherwise prefer to develop and market itself.

Based on its current operating plans, the Company believes its cash, cash equivalents and marketable securities of $342.6 million as of March 31, 2017 will be sufficient to fund its anticipated level of operations and capital expenditures into the second quarter of 2018.

In August 2014, the Financial Accounting Standards Board issued Accounting Standards Update, or ASU, 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40). The guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. After performing this evaluation, the Company believes that it has adequate cash resources to operate for 12 months from the date of issuance of these financial statements.