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Income Taxes - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Income Taxes [Line Items] |  |  |
Total amount of unrecognized tax benefits that would affect the tax rate if recognized | $ 1,400,000 | $ 1,400,000 |
Gross liabilities to expire in 2016 | 579,000 |  |
Deferred tax asset credit tax carryforward resulting from excess tax benefits of share based compensation | 3,000,000 |  |
Deferred tax assets, current |  | 934,000 |
Deferred tax assets, long-term | 18,233,000 | 12,556,000 |
Decrease in net operating loss carryforwards from prior years | 52,400,000 |  |
Tax credit carryforwards | 3,076,000 | $ 2,141,000 |
Tax benefit related to extension of research and development credits | (1,300,000) |  |
Undistributed earning retained indefinitely for reinvestment by foreign subsidiary | 20,600,000 |  |
Accounting Standards Update 2015-17 | Restatement Adjustment |  |  |
Income Taxes [Line Items] |  |  |
Deferred tax assets, current | (900,000) |  |
Deferred tax assets, long-term | $ 900,000 |  |
Ireland |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 25.00% | 25.00% | 25.00%
Ireland | Amarin Pharmaceuticals Ireland Limited |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 12.50% | 12.50% | 12.50%
Ireland | Non-Trading Activity |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 25.00% |  |
Ireland | Trading Activity |  |  |
Income Taxes [Line Items] |  |  |
Corporate tax rate | 12.50% |  |
Republic of Ireland, United Kingdom and Israel |  |  |
Income Taxes [Line Items] |  |  |
Foreign net operating loss carryforwards | $ 565,700,000 |  |
U.S. Federal |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | $ 5,800,000 |  |
U.S. Federal | Minimum |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards, expiration date | 2022 |  |
U.S. Federal | Maximum |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards, expiration date | 2035 |  |
State |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards | $ 1,600,000 |  |
State | Minimum |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards, expiration date | 2022 |  |
State | Maximum |  |  |
Income Taxes [Line Items] |  |  |
Tax credit carryforwards, expiration date | 2035 |  |

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