Description of Business and Basis of Presentation	12 Months Ended
Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Alkermes plc (the “Company”) is a global biopharmaceutical company that seeks to develop innovative medicines in the field of neuroscience. The Company has a portfolio of proprietary commercial products for the treatment of alcohol dependence, opioid dependence, schizophrenia and bipolar I disorder and a pipeline of clinical and preclinical candidates in development for neurological disorders. Headquartered in Dublin, Ireland, the Company has a research and development center in Waltham, Massachusetts; a research and manufacturing facility in Athlone, Ireland; and a manufacturing facility in Wilmington, Ohio. On November 15, 2023, the Company completed the separation of its oncology business into Mural Oncology plc (“Mural”), a new, independent, publicly-traded company (the “Separation”). The Separation was effected by means of a distribution of all of the outstanding ordinary shares of Mural to the Company’s shareholders (the “Distribution”), in which each of the Company’s shareholders received one ordinary share, nominal value $0.01 per share, of Mural for every ten ordinary shares, par value $0.01 per share, of the Company (the “Distribution Ratio”) held by such shareholder as of the close of business on November 6, 2023, the record date for the Distribution (the “Record Date”). The historical results of the oncology business have been reflected as discontinued operations in the Company’s consolidated financial statements through November 15, 2023 (the “Separation Date”). For additional information related to the Separation, see Note 3, Discontinued Operations in these “Notes to Consolidated Financial Statements” in this Annual Report. On December 14, 2023 the Company announced that it entered into a definitive agreement to sell its development and manufacturing facility located in Athlone, Ireland (the “Athlone Facility”) to Novo Nordisk (“Novo”) and plans to enter into subcontracting arrangements to continue certain development and manufacturing activities currently performed at the Athlone Facility for a period of time after the closing of the transaction, which arrangements may continue through the end of 2025. Such transaction is expected to close in mid-2024, subject to certain closing conditions. At December 31, 2023, the Company had classified the assets described under the related asset purchase agreement as “Assets held for sale” within the accompanying consolidated balance sheet.

Description of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Description of Business and Basis of Presentation

1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION

Alkermes plc (the “Company”) is a global biopharmaceutical company that seeks to develop innovative medicines in the field of neuroscience. The Company has a portfolio of proprietary commercial products for the treatment of alcohol dependence, opioid dependence, schizophrenia and bipolar I disorder and a pipeline of clinical and preclinical candidates in development for neurological disorders. Headquartered in Dublin, Ireland, the Company has a research and development center in Waltham, Massachusetts; a research and manufacturing facility in Athlone, Ireland; and a manufacturing facility in Wilmington, Ohio.

On November 15, 2023, the Company completed the separation of its oncology business into Mural Oncology plc (“Mural”), a new, independent, publicly-traded company (the “Separation”). The Separation was effected by means of a distribution of all of the outstanding ordinary shares of Mural to the Company’s shareholders (the “Distribution”), in which each of the Company’s shareholders received one ordinary share, nominal value $0.01 per share, of Mural for every ten ordinary shares, par value $0.01 per share, of the Company (the “Distribution Ratio”) held by such shareholder as of the close of business on November 6, 2023, the record date for the Distribution (the “Record Date”). The historical results of the oncology business have been reflected as discontinued operations in the Company’s consolidated financial statements through November 15, 2023 (the “Separation Date”). For additional information related to the Separation, see Note 3, Discontinued Operations in these “Notes to Consolidated Financial Statements” in this Annual Report.

On December 14, 2023 the Company announced that it entered into a definitive agreement to sell its development and manufacturing facility located in Athlone, Ireland (the “Athlone Facility”) to Novo Nordisk (“Novo”) and plans to enter into subcontracting arrangements to continue certain development and manufacturing activities currently performed at the Athlone Facility for a period of time after the closing of the transaction, which arrangements may continue through the end of 2025. Such transaction is expected to close in mid-2024, subject to certain closing conditions. At December 31, 2023, the Company had classified the assets described under the related asset purchase agreement as “Assets held for sale” within the accompanying consolidated balance sheet.