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Debt - Additional Information (Detail) (USD $)
3 Months Ended 1 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Jan. 31, 2012
May 31, 2014
Dec. 31, 2014
Dec. 31, 2012
Debt Disclosure [Line Items]            
Fair value of embedded derivative liability           $ 14,600,000us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiability
Gain (Loss) on change in fair value of derivative liability 0us-gaap_GainLossOnDerivativeInstrumentsNetPretax 3,500,000us-gaap_GainLossOnDerivativeInstrumentsNetPretax        
Gain (loss) on change in fair value of derivative liability 464,000us-gaap_UnrealizedGainLossOnDerivatives 4,393,000us-gaap_UnrealizedGainLossOnDerivatives        
Interest payment on notes 4,273,000us-gaap_InterestPaid 3,636,000us-gaap_InterestPaid        
Convertible Debt            
Debt Disclosure [Line Items]            
Convertible senior notes, discount 3,500,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Gain (loss) on change in fair value of derivative liability 1,300,000us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible notes, interest expense 2,800,000us-gaap_InterestExpenseDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
2,000,000us-gaap_InterestExpenseDebt
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
       
Interest expense, amortization of discount 1,500,000us-gaap_AmortizationOfDebtDiscountPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
700,000us-gaap_AmortizationOfDebtDiscountPremium
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
       
Interest expense, contractual coupon interest accrual 1,300,000us-gaap_InterestExpenseDebtExcludingAmortization
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
1,300,000us-gaap_InterestExpenseDebtExcludingAmortization
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
       
Accrued interest on convertible note 1,100,000us-gaap_InterestPayableCurrent
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      2,400,000us-gaap_InterestPayableCurrent
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Convertible Debt | 2012 Notes            
Debt Disclosure [Line Items]            
Convertible senior notes, principal amount     150,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
31,300,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Convertible senior notes, stated interest rate     3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
     
Convertible senior notes, due date     2032      
Convertible senior notes, net proceeds     144,300,000us-gaap_ProceedsFromConvertibleDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
     
Convertible senior notes, payment start date     Jul. 15, 2012      
Convertible senior notes, maturity date     Jan. 15, 2032      
Value of shares in excess of principal amount of Notes based on closing price 23,000,000amrn_ExcessPrincipalValueOverFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Additional interest rate on notes per annum 0.50%amrn_AdditionalPercentageInterestRatePenalty
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible senior notes, repurchase price at option of the issuer     100.00%us-gaap_DebtInstrumentRedemptionPricePercentage
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
     
Proceeds allocated to conversion option 23,800,000us-gaap_ProceedsFromDebtNetOfIssuanceCosts
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible senior notes, fair value 26,521,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      25,689,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Note, estimated remaining life 24 months          
Debt discount amortization period 24 months          
Convertible notes, carrying amount net of unamortized discount 31,300,000us-gaap_ConvertibleDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      31,300,000us-gaap_ConvertibleDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Decrease to additional paid-in capital for repurchase of conversion option in convertible notes 10,100,000us-gaap_AdjustmentsToAdditionalPaidInCapitalOther
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible senior notes, discount 0us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      0us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Gain on extinguishment of debt 38,000,000us-gaap_GainsLossesOnExtinguishmentOfDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible Debt | 2012 Notes | American Depository Shares            
Debt Disclosure [Line Items]            
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes 113.4752us-gaap_DebtInstrumentConvertibleConversionRatio1
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember
         
Convertible senior notes, total ADS into which the debt is exchangeable 3,547,916us-gaap_DebtConversionConvertedInstrumentSharesIssued1
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember
         
Convertible Debt | 2012 Notes | Exchanged Debt            
Debt Disclosure [Line Items]            
Convertible senior notes, principal amount       118,700,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtConversionByUniqueDescriptionAxis
= amrn_DebtExchangeMember
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Convertible Debt | 2014 Notes            
Debt Disclosure [Line Items]            
Fair value of embedded derivative liability 1,300,000us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiability
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      2,600,000us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiability
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Convertible senior notes, principal amount       118,700,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Convertible senior notes, stated interest rate       3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Convertible senior notes, due date       2032    
Convertible senior notes, payment start date Jul. 15, 2014          
Convertible senior notes, maturity date Jan. 15, 2032          
Value of shares in excess of principal amount of Notes based on closing price 11,900,000amrn_ExcessPrincipalValueOverFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible senior notes, repurchase price at option of the issuer       100.00%us-gaap_DebtInstrumentRedemptionPricePercentage
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Convertible senior notes, fair value 124,932,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
    90,800,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
75,533,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Convertible notes, carrying amount net of unamortized discount 91,900,000us-gaap_ConvertibleDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
      90,600,000us-gaap_ConvertibleDebt
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
 
Convertible senior notes redemption, end date Jan. 15, 2032          
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, in any number of VWAP Trading days 30us-gaap_DebtInstrumentConvertibleThresholdTradingDays
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible senior notes, discount 27,900,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
    27,900,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Underwriter's fees and offering costs       2,500,000us-gaap_DebtIssuanceCosts
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
   
Gain (loss) on change in fair value of derivative liability 1,300,000us-gaap_UnrealizedGainLossOnDerivatives
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
         
Convertible Debt | 2014 Notes | American Depository Shares            
Debt Disclosure [Line Items]            
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes 384.6154us-gaap_DebtInstrumentConvertibleConversionRatio1
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember
         
Convertible senior notes, total ADS into which the debt is exchangeable 45,666,925us-gaap_DebtConversionConvertedInstrumentSharesIssued1
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember
         
Convertible senior notes, initial exchange price $ 2.60us-gaap_DebtInstrumentConvertibleConversionPrice1
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementClassOfStockAxis
= amrn_AmericanDepositorySharesMember
         
Convertible Debt | 2014 Notes | Minimum            
Debt Disclosure [Line Items]            
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price 110.00%us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
         
Convertible senior notes, mandatory exchange in whole or in part if daily VWAP equals or exceeds percentage of exchange price, at least number of VWAP Trading days 20 days          
Convertible Debt | Finance            
Debt Disclosure [Line Items]            
Interest payment on notes 2,600,000us-gaap_InterestPaid
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_SecuritiesFinancingTransactionAxis
= amrn_FinanceMember
      2,600,000us-gaap_InterestPaid
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_SecuritiesFinancingTransactionAxis
= amrn_FinanceMember
 
Convertible Debt | Other debt outstanding | 2012 Notes            
Debt Disclosure [Line Items]            
Convertible senior notes, fair value 126,200,000us-gaap_DebtInstrumentFairValue
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesOneMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= amrn_OtherDebtObligationsMember
         
Convertible Debt | Non Cash | 2014 Notes            
Debt Disclosure [Line Items]            
Convertible senior notes, discount 26,800,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementScenarioAxis
= amrn_NonCashMember
      28,200,000us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= amrn_SeniorNotesTwoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleDebtMember
/ us-gaap_StatementScenarioAxis
= amrn_NonCashMember
 
Biopharma Debt            
Debt Disclosure [Line Items]            
Amount received at the closing of the agreement           100,000,000us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
Maximum repayment of future revenue and receivables 142,700,000us-gaap_OtherCommitment
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
        150,000,000us-gaap_OtherCommitment
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
Repayment under agreement 1,600,000amrn_GuaranteePayments
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
         
Biopharma Debt | Cash            
Debt Disclosure [Line Items]            
Interest expense 1,700,000us-gaap_InterestExpense
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
/ us-gaap_StatementScenarioAxis
= amrn_ChargesCashMember
1,900,000us-gaap_InterestExpense
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
/ us-gaap_StatementScenarioAxis
= amrn_ChargesCashMember
       
Biopharma Debt | Non Cash            
Debt Disclosure [Line Items]            
Interest expense 500,000us-gaap_InterestExpense
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
/ us-gaap_StatementScenarioAxis
= amrn_NonCashMember
500,000us-gaap_InterestExpense
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
/ us-gaap_StatementScenarioAxis
= amrn_NonCashMember
       
Biopharma Debt | May 2015            
Debt Disclosure [Line Items]            
Future minimum repayment under agreement 1,600,000amrn_FutureMinimumGuaranteePayments
/ amrn_PeriodAxis
= amrn_PeriodOneMember
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
         
Biopharma Debt | Third quarter of 2015 and in each of the next two quarters            
Debt Disclosure [Line Items]            
Future minimum repayment under agreement 10,000,000amrn_FutureMinimumGuaranteePayments
/ amrn_PeriodAxis
= amrn_PeriodTwoMember
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
         
Biopharma Debt | Per quarter in each of the next four quarters            
Debt Disclosure [Line Items]            
Future minimum repayment under agreement 15,000,000amrn_FutureMinimumGuaranteePayments
/ amrn_PeriodAxis
= amrn_PeriodThreeMember
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember
         
Biopharma Debt | Final Payment            
Debt Disclosure [Line Items]            
Future minimum repayment under agreement $ 13,000,000amrn_FutureMinimumGuaranteePayments
/ amrn_PeriodAxis
= amrn_PeriodFourMember
/ us-gaap_StatementBusinessSegmentsAxis
= amrn_BiopharmaceuticalMember