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Equity - Common Stock - Additional Information (Detail) - £ / shares
 6 Months Ended
Mar. 16, 2020
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Mar. 05, 2015
Stockholders Equity Note [Line Items]          
Common stock, par value   £ 0.50   £ 0.50 £ 0.50
2011 Plan          
Stockholders Equity Note [Line Items]          
Number of shares remaining under the plan   2,634,440      
Amarin Corporation Plc 2017 Employee Stock Purchase Plan | Ordinary Shares          
Stockholders Equity Note [Line Items]          
Issuance of stock (shares)   123,608 47,358    
American Depositary Shares | Stock Incentive Plan 2020          
Stockholders Equity Note [Line Items]          
Expiration date of stock incentive plan 2030-07        
American Depositary Shares | Stock Incentive Plan 2020 | Ordinary Shares          
Stockholders Equity Note [Line Items]          
Common stock, par value £ 0.50        
Issuance of stock (shares) 20,000,000