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Income Taxes - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Income Taxes [Line Items]      
Total amount of unrecognized tax benefits that would affect the tax rate if recognized $ 1,700,000 $ 1,200,000  
Gross liabilities to expire in 2014 254,000    
Tax credit carryforwards 1,256,000 5,000  
Discrete income tax benefit to be recognized in the first quarter of 2013 1,900,000    
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 528,200,000    
U.S. Federal
      
Income Taxes [Line Items]      
Tax credit carryforwards 4,100,000    
U.S. Federal | Ester Neurosciences Ltd | Minimum
      
Income Taxes [Line Items]      
U.S Federal tax credit carryforwards, expiration date 2029    
U.S. Federal | Ester Neurosciences Ltd | Maximum
      
Income Taxes [Line Items]      
U.S Federal tax credit carryforwards, expiration date 2032    
State
      
Income Taxes [Line Items]      
Tax credit carryforwards $ 1,800,000