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Subsequent Events - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 12 Months Ended 0 Months Ended
Dec. 31, 2014
Feb. 26, 2015
Jan. 29, 2015
Subsequent Event [Line Items]      
Granted options 3,271,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod    
Subsequent Event | Eddingpharm      
Subsequent Event [Line Items]      
Non-refundable up-front received   $ 15.0amrn_NonRefundableUpfrontPaymentsReceived
/ amrn_BusinessDevelopmentsAxis
= amrn_EddingpharmMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		  
Subsequent Event | Eddingpharm | Maximum      
Subsequent Event [Line Items]      
Additional upfront payment eligible to receive based on development, regulatory and sales Milestone   $ 154.0amrn_EligibleMilestonePayment
/ amrn_BusinessDevelopmentsAxis
= amrn_EddingpharmMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		  
Subsequent Event | Restricted Stock Units (RSUs)      
Subsequent Event [Line Items]      
Granted options     2,564,251us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Vesting period     3 years
Subsequent Event | Stock options      
Subsequent Event [Line Items]      
Granted options     1,622,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockOptionMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Vesting period     4 years