Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying condensed consolidated financial statements of the Company for the three and nine months ended September 30, 2024 and 2023 are unaudited and have been prepared on a basis substantially consistent with the audited financial statements for the year ended December 31, 2023. The year-end consolidated balance sheet data, which is presented for comparative purposes, was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the U.S. (commonly referred to as “GAAP”). In the opinion of management, the condensed consolidated financial statements include all adjustments of a normal recurring nature that are necessary to state fairly the results of operations for the reported periods. These financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto of the Company, which are contained in the Annual Report. The results of the Company’s operations for any interim period are not necessarily indicative of the results of the Company’s operations for any other interim period or for any full fiscal year. Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of Alkermes plc and its wholly-owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies in the “Notes to Consolidated Financial Statements” accompanying the Annual Report. Intercompany accounts and transactions have been eliminated. Columns and rows within tables may not sum due to rounding. Reclassification The Company has presented operations from its former oncology business as discontinued operations in the accompanying condensed consolidated statement of operations and comprehensive income for the three and nine months ended September 30, 2023. See Note 3, Discontinued Operations in these “Notes to Condensed Consolidated Financial Statements” in this Form 10-Q for additional information. Discontinued Operations The Company determined that the separation of its oncology business in November 2023 met the criteria for classification of the oncology business as discontinued operations in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 205, Discontinued Operations (“Topic 205”). Accordingly, the financial statements have been updated to present the results of the oncology business as discontinued operations for the three and nine months ended September 30, 2023 in the accompanying condensed consolidated statement of operations and comprehensive income. Assets Held for Sale In connection with the sale of the Athlone Facility, the Company reviewed FASB ASC 805, Business Combinations (“Topic 805”) and, based on the definitions therein, determined that the Athlone Facility constituted a business. Accordingly, the assets associated with the sale of the Athlone Facility were classified as “Assets held for sale” in the accompanying condensed consolidated balance sheet as of December 31, 2023. Use of Estimates The preparation of the Company’s condensed consolidated financial statements in accordance with GAAP requires that Company management make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies, including, but not limited to, those related to revenue from contracts with its customers and related allowances, impairment and amortization of long-lived assets, share-based compensation, income taxes including the valuation allowance for deferred tax assets, valuation of investments and litigation. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different conditions or using different assumptions. Segment Information The Company operates as one business segment, which is the business of developing, manufacturing and commercializing medicines designed to address unmet medical needs of patients in major therapeutic areas. The Company’s chief decision maker, its Chief Executive Officer and chairman of its board of directors, reviews the Company’s operating results on an aggregate basis and manages the Company’s operations as a single operating unit. New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard-setting bodies that are adopted by the Company on or prior to the specified effective date. Unless otherwise described in this Form 10-Q, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption. In November 2023, the FASB issued Accounting Standards Update (“ASU”) 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosure, which requires disclosure of significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss, an amount and description of its composition for other segment items to reconcile to segment profit or loss and the title and position of the Company’s chief operating decision maker. The amendments in this guidance also expand the interim segment disclosure requirements. All disclosure requirements under this guidance are required for public entities with a single reportable segment. This ASU became effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted and the amendments in this guidance are required to be applied on a retrospective basis. The Company elected to early adopt this guidance and determined this ASU did not have an impact on its consolidated financial statements and related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, to enhance the transparency and decision usefulness of income tax disclosures in order to provide information to assist key stakeholders in better assessing how the Company’s operations and related tax risks and tax planning and operational opportunities affect the Company’s tax rate and prospects for future cash flows. This ASU becomes effective for public companies for annual periods beginning after December 15, 2024. Early adoption is permitted for annual financial statements that have not yet been issued or made available for issuance. This guidance will be applied on a prospective basis. The Company is currently evaluating the impact this ASU will have on its consolidated financial statements and related disclosures.