Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements of the Company for the three and six months ended June 30, 2023 and 2022 are unaudited and have been prepared on a basis substantially consistent with the audited financial statements for the year ended December 31, 2022. The year-end condensed 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 Company’s 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	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 Company’s Annual Report. Intercompany accounts and transactions have been eliminated.
Use of Estimates	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 intangibles and 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	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	New Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board or other standard-setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued accounting pronouncements that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

Basis of Presentation

The accompanying condensed consolidated financial statements of the Company for the three and six months ended June 30, 2023 and 2022 are unaudited and have been prepared on a basis substantially consistent with the audited financial statements for the year ended December 31, 2022. The year-end condensed 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 Company’s 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.

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 intangibles and 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.

New Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board or other standard-setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued accounting pronouncements that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.