| Document and Entity Information - USD ($) | 12 Months Ended | ||
| Dec. 31, 2022 | Apr. 21, 2023 | Jun. 30, 2022 | |
| Cover [Abstract] | |||
| Entity Registrant Name | Alkermes plc. | ||
| Entity Central Index Key | 0001520262 | ||
| Document Type | 10-K/A | ||
| Document Period End Date | Dec. 31, 2022 | ||
| Amendment Flag | true | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | false | ||
| ICFR Auditor Attestation Flag | true | ||
| Entity Shell Company | false | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Large Accelerated Filer | ||
| Entity Public Float | $ 4,838,408,388 | ||
| Entity Common Stock, Shares Outstanding | 166,121,384 | ||
| Document Fiscal Year Focus | 2022 | ||
| Document Fiscal Period Focus | FY | ||
| Trading Symbol | ALKS | ||
| Entity Well-known Seasoned Issuer | Yes | ||
| Entity Voluntary Filers | No | ||
| Entity File Number | 001-35299 | ||
| Entity Incorporation, State or Country Code | L2 | ||
| Entity Tax Identification Number | 98-1007018 | ||
| Entity Address, Address Line One | Connaught House | ||
| Entity Address, Address Line Two | 1 Burlington Road | ||
| Entity Address, City or Town | Dublin 4 | ||
| Entity Address, Country | IE | ||
| Entity Address, Postal Zip Code | D04 C5Y6 | ||
| City Area Code | 353 | ||
| Local Phone Number | 1-772-8000 | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Title of 12(b) Security | Ordinary shares, $0.01 par value | ||
| Security Exchange Name | NASDAQ | ||
| Amendment Description | This Amendment No. 1 to Annual Report on Form 10-K/A (this “Amendment”), amends the Annual Report on Form 10-K for the fiscal year ended December 31, 2022 (Commission File Number 001-35299), as filed by the registrant with the U.S. Securities and Exchange Commission (the “SEC”) on February 16, 2023 (the “2022 Annual Report”). The principal purpose of this Amendment is to amend Part III of the 2022 Annual Report to include the information that was intended to be incorporated therein by reference to the registrant’s definitive proxy statement for its 2023 annual general meeting of shareholders, and to update certain of the information included on the cover page of the 2022 Annual Report and in Item 15 and the Exhibit Index of the 2022 Annual Report. This Amendment hereby amends the cover page, Part III (Items 10 through 14) and Part IV (Item 15) of the 2022 Annual Report. In addition, as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), new certifications by the registrant’s principal executive officer and principal financial officer are filed as exhibits to this Amendment. No attempt has been made in this Amendment to modify or update the other disclosures presented in the 2022 Annual Report. This Amendment does not reflect events occurring after the filing of the 2022 Annual Report (i.e., those events occurring after February 16, 2023) or modify or update those disclosures that may be affected by subsequent events. Accordingly, this Amendment should be read in conjunction with the 2022 Annual Report and the registrant’s other filings with the SEC. | ||
| Auditor Name | PricewaterhouseCoopers LLP | ||
| Auditor Location | Boston Massachusetts | ||
| Auditor Firm ID | 238 | ||
| Documents Incorporated by Reference | None. |
