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Equity - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 12 Months Ended 0 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 11, 2014
Jan. 08, 2014
Jan. 31, 2013
Stockholders Equity Note [Line Items]            
Refund of equity issuance costs $ 3,191amrn_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCostsRefund          
Shares issued, exercise of stock options 234,500us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 386,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised        
Proceeds from exercise of stock options, net of transaction costs 307us-gaap_ProceedsFromStockOptionsExercised 627us-gaap_ProceedsFromStockOptionsExercised 8,205us-gaap_ProceedsFromStockOptionsExercised      
Shares issued, exercise of warrants 1,684,888amrn_StockIssuedDuringPeriodSharesStockWarrantsExercised 147,050amrn_StockIssuedDuringPeriodSharesStockWarrantsExercised        
Proceeds from exercise of warrants, net of transaction costs $ 1,651us-gaap_ProceedsFromWarrantExercises $ 160us-gaap_ProceedsFromWarrantExercises $ 16,720us-gaap_ProceedsFromWarrantExercises      
Stock options, Granted 3,271,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod          
Stock Incentive Plan 2011            
Stockholders Equity Note [Line Items]            
Stock options, Granted       205,890us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		 2,605,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		  
Stock options, Vesting Period 4 years          
Stock Incentive Plan 2011 | Group 2            
Stockholders Equity Note [Line Items]            
Restricted stock units, issued as a result of vesting   0us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember
/ us-gaap_StatementScenarioAxis
= amrn_Group2Member		        
Stock Incentive Plan 2011 | Restricted Stock Units (RSUs)            
Stockholders Equity Note [Line Items]            
Stock units, Granted       173,348us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		 2,082,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		 454,875us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember
Stock options, Vesting Period         3 years  
Stock Incentive Plan 2011 | Stock Options            
Stockholders Equity Note [Line Items]            
Stock options, Vesting Period         4 years