Equity - Preferred Stock - Additional Information (Detail)				3 Months Ended		12 Months Ended
	Jul. 10, 2015 USD ($) $ / shares shares	Mar. 30, 2015 USD ($)	Mar. 05, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2017 £ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 £ / shares shares	Mar. 05, 2015 £ / shares
Stockholders Equity Note [Line Items]
Preferred stock, par value | £ / shares						£ 0.05				£ 0.05	£ 0.05
Private placement, closing date			Mar. 30, 2015
Stock issued under private placement, value							$ 64,613,000
Aggregate gross proceeds					$ 52,800,000
Estimated offering expense					$ 700,000
Common stock, par value | £ / shares						£ 0.50				£ 0.50	£ 0.50
Number of shares issued for each preference shares | shares			0.1
Preferred stock, equivalent ordinary shares upon future consolidation outstanding | shares						32,818,464			32,818,464	32,818,464
Market value, per share | $ / shares			$ 2.39
BCF resulting from issuance of Series A Preference Shares				$ 31,300,000				$ 32,987,000
Second Private Placement | Preferred Stock Purchase Option
Stockholders Equity Note [Line Items]
BCF resulting from issuance of Series A Preference Shares								3,400,000
Derivative liability at fair value		$ 1,800,000	$ 900,000
Gain (loss) on change in fair value of derivatives			$ (900,000)					(1,600,000)
Transfer derivative liability to equity		$ 1,800,000
Series A Preferred Stock
Stockholders Equity Note [Line Items]
American depositary shares conversion rate to preference shares						American Depositary Shares, each representing one (1) share of Amarin’s Series A Convertible Preference Shares
Stock issued under private placement, value								$ 57,853,000
Series A Preferred Stock | Minimum
Stockholders Equity Note [Line Items]
Beneficial ownership limitation			4.99%
Series A Preferred Stock | Maximum
Stockholders Equity Note [Line Items]
Beneficial ownership limitation			19.90%
Series A Preferred Stock | Maximum | Second Private Placement
Stockholders Equity Note [Line Items]
Preferred stock, equivalent ordinary shares upon future consolidation outstanding | shares	3,886,718
Ordinary Shares
Stockholders Equity Note [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable | shares								6,283,333
Preferred stock, equivalent ordinary shares upon future consolidation outstanding | shares						32,818,464			32,818,464
American Depositary Shares | Series A Preferred Stock
Stockholders Equity Note [Line Items]
Issuance of stock (shares) | shares			352,150,790
Stock issued under private placement, value			$ 52,800,000
American Depositary Shares | Series A Preferred Stock | Second Private Placement
Stockholders Equity Note [Line Items]
Issuance of stock (shares) | shares	38,867,180
Stock issued under private placement, value	$ 5,800,000
Preferred Shares Basis
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares			$ 0.15
Preferred Shares Basis | Series A Preferred Stock | Second Private Placement
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares	$ 0.15
Ordinary Shares Basis
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares			$ 1.50						$ 1.50
Ordinary Shares Basis | Series A Preferred Stock | Second Private Placement
Stockholders Equity Note [Line Items]
Share conversion price | $ / shares	$ 1.50