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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Income Taxes [Line Items] |  |  |
Total amount of unrecognized tax benefits that would affect the tax rate if recognized | $ 1,000,000 | $ 500,000 |
Gross liabilities to expire in 2012 | 48,000 |  |
Corporate tax rate | 25.00% | 25.00% | 25.00%
Tax credit carryforwards | 6,000 | 30,000 |
Ester Neurosciences Ltd |  |  |
Income Taxes [Line Items] |  |  |
Net operating losses that are not likely to be realized in the future | 12,000,000 |  |
Ireland | Non-Trading Activity |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate in Ireland for trading and non-trading activities | 25.00% |  |
Ireland | Trading Activity | Amarin Pharmaceuticals Ireland Limited |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate in Ireland for trading and non-trading activities | 12.50% |  |
Republic of Ireland, United Kingdom and Israel |  |  |
Income Taxes [Line Items] |  |  |
Foreign net operating loss carryforwards | 175,700,000 |  |
U.S. Federal |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | 1,200,000 |  |
U.S. Federal | Ester Neurosciences Ltd | Minimum |  |  |
Income Taxes [Line Items] |  |  |
U.S Federal tax credit carryforwards, expiration date | 2028 |  |
U.S. Federal | Ester Neurosciences Ltd | Maximum |  |  |
Income Taxes [Line Items] |  |  |
U.S Federal tax credit carryforwards, expiration date | 2030 |  |
State |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | $ 1,400,000 |  |
Foreign Country |  |  |
Income Taxes [Line Items] |  |  |
Foreign net operating loss carryforwards, expiration date | 2011 |  |

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- Definition The tax effect as of the balance sheet date of the amount of excess of tax deductions over gross income in a year which cannot be used on the tax return of a country outside the country of domicile in the current year but can be carried forward to reduce taxable income or income taxes payable in a future year, for which there must be sufficient tax-basis income to utilize a portion or all of the carryforward amount to realize the deferred tax asset. + References Reference 1: 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=6969291&loc=d3e28680-109314 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 43, 289 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: 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 4: 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 + Details
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