Equity - Preferred Stock - Additional Information (Detail)		1 Months Ended	3 Months Ended
	Mar. 05, 2015 USD ($) shares	Apr. 30, 2020 shares	Mar. 31, 2020 £ / shares shares	Mar. 31, 2015 USD ($)	Dec. 31, 2019 £ / shares shares	Mar. 05, 2015 £ / shares shares	Mar. 05, 2015 $ / shares shares
Stockholders Equity Note [Line Items]
Preferred stock, par value | £ / shares			£ 0.05		£ 0.05	£ 0.05
Private placement, closing date	Mar. 30, 2015
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						0.1	0.1
Preferred stock, equivalent ordinary shares upon future consolidation outstanding			28,931,746		28,931,746
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
Series A Preferred Stock | Subsequent Event
Stockholders Equity Note [Line Items]
Conversion of stock, shares converted		237,713,680
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%
Ordinary Shares
Stockholders Equity Note [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable			6,283,333
Preferred stock, equivalent ordinary shares upon future consolidation outstanding			28,931,746
Ordinary Shares | Subsequent Event
Stockholders Equity Note [Line Items]
Convertible senior notes, total ADS into which the debt is exchangeable		23,771,368
Preferred stock, equivalent ordinary shares upon future consolidation outstanding		5,160,378
American Depositary Shares | Series A Preferred Stock
Stockholders Equity Note [Line Items]
Issuance of stock (shares)	352,150,790
Stock issued under private placement, value | $	$ 52,800,000
Preferred Shares Basis
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