Contingent CVR payment.

No definition available.

Name:	alks_ContingentCVRPayment
Namespace Prefix:	alks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Employee service share based compensation allocation of recognized period costs capitalized amounts.

+ References

No definition available.

+ Details

Name:	alks_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmounts
Namespace Prefix:	alks_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479983/718-10-S45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479830/718-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_TitleOfIndividualAxis=alks_FormerChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=alks_AvadelPharmaceuticalsPlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementOfFinancialPositionLocationBalanceAxis=us-gaap_InventoryNet
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementOfFinancialPositionLocationBalanceAxis=us-gaap_OtherAssetsNoncurrent
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Share-based Compensation - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 26,747,000	$ 24,664,000	$ 94,216,000	$ 72,441,000
Former Alkermes CEO
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Incremental share-based compensation expense related to certain equity awards	400,000		5,000,000
Avadel Pharmaceuticals Plc
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	0		18,400,000
Contingent CVR payment to former employees			2,200,000
Avadel Pharmaceuticals Plc \| Maximum
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Contingent CVR payment to former employees	100,000
Location, Statement of Financial Position, Balance [Axis]: us-gaap:InventoryNet
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation cost capitalized	3,500,000		3,500,000		$ 3,200,000
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation cost capitalized	$ 3,100,000		$ 3,100,000		$ 1,600,000