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Equity - Additional Information (Detail)
 0 Months Ended 3 Months Ended 3 Months Ended 0 Months Ended 0 Months Ended
Mar. 05, 2015
Mar. 31, 2015
USD ($)
Mar. 31, 2014
USD ($)
Mar. 31, 2015
GBP (£)
Dec. 31, 2014
GBP (£)
Mar. 31, 2015
Preferred Stock Purchase Option
USD ($)
Mar. 31, 2015
Minimum
Mar. 31, 2015
Maximum
Mar. 05, 2015
American Depository Shares
USD ($)
Mar. 31, 2015
American Depository Shares
USD ($)
Mar. 30, 2015
American Depository Shares
USD ($)
Mar. 30, 2015
Series A Preferred Stock
Mar. 05, 2015
Series A Preferred Stock
GBP (£)
Mar. 31, 2015
Employee tax obligations
Jan. 29, 2015
Restricted Stock Units (RSUs)
Subsequent Event
Jan. 29, 2015
Stock options
Subsequent Event
Mar. 11, 2014
Stock Incentive Plan 2011
Jan. 29, 2015
Stock Incentive Plan 2011
Restricted Stock Units (RSUs)
Mar. 11, 2014
Stock Incentive Plan 2011
Restricted Stock Units (RSUs)
Jan. 29, 2015
Stock Incentive Plan 2011
Stock Options
Stockholders Equity Note [Line Items]                                        
Shares issued, exercise of warrants   1,844,585amrn_StockIssuedDuringPeriodSharesStockWarrantsExercised                                    
Proceeds from exercise of warrants, gross of transaction costs   $ 2,800,000amrn_ProceedsFromWarrantExercisesGross                                    
Proceeds from exercise of warrants, net of transaction costs   2,713,000us-gaap_ProceedsFromWarrantExercises                                    
Shares issued, exercise of stock options   2,114us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised 215,000us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised                                  
Proceeds from exercise of stock options, net of transaction costs   4,000us-gaap_ProceedsFromStockOptionsExercised 285,000us-gaap_ProceedsFromStockOptionsExercised                                  
Stock units, Granted                                   2,564,251us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		 173,348us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		  
Granted options                             2,082,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		 2,605,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_StockOptionMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		 205,890us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember		     1,622,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= amrn_StockIncentivePlanTwentyElevenMember
Stock options, Vesting Period                             3 years 4 years   3 years   4 years
Shares issued, related to the vesting of RSUs   639,500amrn_StockIssuedDuringPeriodShareExerciseOfStockOptionsVestingOfRestrictedStock                                    
Treasury shares   134,337us-gaap_TreasuryStockShares     20,079us-gaap_TreasuryStockShares                 114,258us-gaap_TreasuryStockShares
/ amrn_TypeofObligationAxis
= amrn_TaxSharingAgreementObligationMember		            
Stock issued under private placement, value   52,253,000us-gaap_StockIssuedDuringPeriodValueNewIssues             52,800,000us-gaap_StockIssuedDuringPeriodValueNewIssues
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember		                      
American depositary shares conversion rate to preference shares   1us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion                   1us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesAPreferredStockMember		 1us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesAPreferredStockMember		              
Preference Shares, par value       £ 0.05us-gaap_PreferredStockParOrStatedValuePerShare £ 0.05us-gaap_PreferredStockParOrStatedValuePerShare               £ 0.05us-gaap_PreferredStockParOrStatedValuePerShare
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesAPreferredStockMember		              
Private placement, closing date Mar. 30, 2015                                      
Share, negotiated price                   $ 150,000amrn_NegotiatedPurchasePricePerUnit
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember		                    
Share conversion price   $ 1.50amrn_ConversionPricePerShare               $ 1,500,000amrn_ConversionPricePerShare
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember		                    
Aggregate gross proceeds   52,800,000us-gaap_ProceedsFromIssuanceOfPrivatePlacement                                    
Estimated offering expense   600,000amrn_OtherEstimatedOfferingCosts                                    
Preference shares conversion rate to ordinary share   10.00%amrn_PercentageRepresentationOfCommonStockOutstandingUponConversion                                    
Common stock, par value       £ 0.50us-gaap_CommonStockParOrStatedValuePerShare £ 0.50us-gaap_CommonStockParOrStatedValuePerShare                              
Beneficial ownership limitation             4.99%amrn_BeneficialOwnershipLimitationPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 19.90%amrn_BeneficialOwnershipLimitationPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                        
Share maximum amount   35,215,079us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased                                    
Market value, per share   $ 2.39us-gaap_SharePrice                                    
BCF resulting from issuance of Series A Preference Shares   31,300,000us-gaap_DebtInstrumentConvertibleBeneficialConversionFeature                                    
Additional shares purchase amount                     5,800,000amrn_ShareRepurchaseProgramAdditionalAuthorizedAmount
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember		                  
Preferred stock purchase option derivative liability at fair value           900,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= amrn_PreferredStockPurchaseOptionMember		                            
Gain (loss) on change in fair value of derivatives           900,000us-gaap_DerivativeGainLossOnDerivativeNet
/ us-gaap_DerivativeInstrumentRiskAxis
= amrn_PreferredStockPurchaseOptionMember		                            
Transfer derivative liability to equity   $ 1,814,000amrn_DerivativeLiabilitiesTransferredToStockholdersEquity       $ 1,814,000amrn_DerivativeLiabilitiesTransferredToStockholdersEquity
/ us-gaap_DerivativeInstrumentRiskAxis
= amrn_PreferredStockPurchaseOptionMember