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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Income Taxes [Line Items] |  |  |
Total amount of unrecognized tax benefits that would affect the tax rate if recognized | 1,400,000 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate | 1,700,000 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate |
Gross liabilities to expire in 2015 | 439,000 amrn_DeferredTaxLiabilitiesSubjectToExpiration |  |
Decrease in net operating loss carryforwards from prior years | 14,900,000 amrn_DeferredTaxAssetsOperatingLossCarryforwardsChangeInAmount |  |
Tax credit carryforwards | 2,141,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards | 1,256,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards |
Income tax benefit to be recognized in the fourth quarter of 2014 | 1,400,000 us-gaap_OtherTaxExpenseBenefit |  |
Ireland |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 25.00%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE | 25.00%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE | 25.00%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE
Ireland | Amarin Pharmaceuticals Ireland Limited |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 12.50%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE / dei_LegalEntityAxis = amrn_AmarinPharmaceuticalsIrelandLimitedMember | 12.50%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE / dei_LegalEntityAxis = amrn_AmarinPharmaceuticalsIrelandLimitedMember | 12.50%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE / dei_LegalEntityAxis = amrn_AmarinPharmaceuticalsIrelandLimitedMember
Ireland | Non-Trading Activity |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 25.00%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE / amrn_TaxesByNatureAxis = amrn_NonTradingActivityMember |  |
Ireland | Trading Activity |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 12.50%amrn_StatutoryTaxRate / us-gaap_IncomeTaxAuthorityAxis = country_IE / amrn_TaxesByNatureAxis = amrn_TradingActivityMember |  |
Republic of Ireland, United Kingdom and Israel |  |  |
Income Taxes [Line Items] |  |  |
Foreign net operating loss carryforwards | 513,300,000 us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign / us-gaap_IncomeTaxAuthorityAxis = amrn_RepublicOfIrelandUnitedKingdomAndIsraelMember |  |
U.S. Federal |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | 6,200,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_DomesticCountryMember |  |
U.S. Federal | Ester Neurosciences Ltd | Minimum |  |  |
Income Taxes [Line Items] |  |  |
U.S Federal tax credit carryforwards, expiration date | 2020 |  |
U.S. Federal | Ester Neurosciences Ltd | Maximum |  |  |
Income Taxes [Line Items] |  |  |
U.S Federal tax credit carryforwards, expiration date | 2034 |  |
State |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | 1,400,000 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |  |

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- Definition Deferred Tax Liabilities, Subject to Expiration + References No definition available. + Details
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- Definition Statutory Tax Rate + References No definition available. + Details
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible foreign operating loss carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314 + Details
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- Definition The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 + Details
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- Definition Amount of other income tax expense (benefit). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32672-109319 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(1)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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