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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