SUBSEQUENT EVENTS (unaudited)	12 Months Ended
SUBSEQUENT EVENTS (unaudited)	Dec. 31, 2019
Subsequent Events [Abstract]
SUBSEQUENT EVENTS (unaudited)	SUBSEQUENT EVENTS (unaudited) In connection with the amendment of our financial statements, we have evaluated subsequent events through the date the financial statements were available to be reissued. May 2020 Restructuring In May 2020, we completed a restructuring to reduce the size of our organization in conjunction with the planned divestiture of Intrarosa and Vyleesi and expected declines in our revenue due to the COVID-19 pandemic. Approximately 110 employees were displaced through this workforce reduction. We recorded a one-time restructuring charge of $8.2 million primarily related to severance and related benefits on our condensed consolidated statement of operations during the second quarter of 2020 and expect the restructuring charges incurred to date under this program to be substantially paid in cash by the end of the second quarter of 2021. Sale of Intrarosa On May 21, 2020, we sold our rights to commercialize and have manufactured Intrarosa in the United States to Millicent Pharma Limited (“Millicent”) pursuant to an Asset Purchase Agreement between the Company and Millicent, dated May 21, 2020. Under the terms of the Asset Purchase Agreement, we received an upfront payment of $20.9 million in cash, subject to customary purchase price adjustments, including in connection with the transfer of certain inventory. We are eligible to receive up to $105.0 million in aggregate milestone payments upon the achievement of certain sales milestones, namely: (a) $25.0 million the first time net sales during any consecutive twelve month period exceeds $65.0 million, (b) $35.0 million the first time net sales during any consecutive twelve month period exceeds $115.0 million and (c) $45.0 million the first time net sales during any consecutive twelve month period exceeds $175.0 million. We recognized a Gain on Sale of Assets of $14.4 million on our condensed consolidated statements of operations for the three and six months ended June 30, 2020 related to this transaction. Cessation of the AMAG-423 Study In July 2020, we decided to stop the AMAG-423 Phase 2b/3a study. This decision was based primarily on the independent Data Safety Monitoring Board’s (the “DSMB”) unanimous recommendation to stop the study following an interim analysis of the data collected to date in the study, which analysis we asked the DSMB to conduct due to extended and ongoing delays in enrollment of the trial (based primarily on the effect of COVID-19 on clinical trial research and the nature of the patient population). There were no safety concerns raised during this study and safety was not a contributing factor to our decision to terminate the study. We are currently focused on ensuring an appropriate closeout of the study in partnership with investigators and other relevant stakeholders. In connection with the cessation of the AMAG-423 Phase 2b/3a study, on August 6, 2020, we terminated our supply agreement (including termination of significant minimum purchase obligations) with our third party supplier in exchange for a one-time payment by us of $12.5 million and our grant to our third party supplier of a 9-month option (subject to extension under certain situations) to acquire the AMAG-423 program rights and assume our related obligations, including our obligations under the Velo Option Agreement. License to Develop and Commercialize ciraparantag in Europe, Australia and New Zealand In July 2020, we entered into a License and Commercialization Agreement with Norgine B.V. (“Norgine”, and such agreement, the “Norgine Agreement”), pursuant to which we granted Norgine an exclusive license to develop and commercialize ciraparantag in certain countries in Europe, Australia and New Zealand. We received a $30.0 million upfront payment upon signing. In addition, pursuant to the terms and conditions of the Norgine Agreement (a) Norgine will pay us one- third of the actual and reasonable out-of-pocket costs of the Phase 3 program, pursuant to a mutually agreed upon budget, (b) we are eligible to receive up to $70.0 million upon the achievement of certain regulatory milestones (of which we will pay $40.0 million to the former equity holders of Perosphere pursuant to the terms of the Perosphere Agreement), (c) we are eligible to receive up to $190.0 million contingent upon meeting certain sales milestones, and (d) Norgine will pay us tiered double-digit royalties on net sales in the licensed territory. We will be responsible for manufacturing and supplying Norgine with its requirements of clinical and commercial product pursuant to supply agreement(s) to be entered into by the parties. Settlement On July 14, 2020, we entered into a Confidential Settlement Agreement and Release with a third-party manufacturer to resolve outstanding disputes. Pursuant to this agreement, we were paid a sum of $17.4 million, and the parties exchanged mutual releases to resolve all disputes between them. Termination of the Palatin Agreement In July 2020, we entered into a termination agreement with Palatin detailing the terms and conditions for the termination of our rights and obligations to develop and commercialize Vyleesi under the Palatin License Agreement and for the transfer of full ownership of Vyleesi to Palatin (the “Termination Agreement”). In accordance with the terms of the Termination Agreement, we transferred and assigned to Palatin the regulatory approval for Vyleesi, inventory, certain third party contracts, intellectual property rights and regulatory files and commercial materials of AMAG related to Vyleesi in the AMAG Territory. In consideration for the early termination of the License Agreement, the assumption of certain liabilities by Palatin (including significant minimum purchase obligations), and in lieu of any future milestone payments, royalties and other payments by AMAG to Palatin contemplated by the Palatin License Agreement, we paid Palatin $12.0 million following the termination, and we will pay an additional $4.3 million on March 31, 2021. In addition, we agreed to provide certain transitional services to Palatin for a period of time following the closing pursuant to a transition services agreement.