Development, Commercialization and Supply Agreement - Recognized Revenues Changes in Contract Asset and Contract Liability Balances (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Revenue recognized in the period from:
Amounts included in contract liability at the beginning of the period	$ 547

Contract with customer liability revenue recognized excluding performance obligation satisfied in previous period.

No definition available.

Name:	amrn_ContractWithCustomerLiabilityRevenueRecognizedExcludingPerformanceObligationSatisfiedInPreviousPeriod
Namespace Prefix:	amrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration