Equity - Preferred Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2015 USD ($) shares	Mar. 31, 2015 USD ($)	Dec. 31, 2021 £ / shares shares	Dec. 31, 2020 £ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 shares	Dec. 31, 2015 shares	Mar. 31, 2015 £ / shares	Mar. 31, 2015 $ / shares
Stockholders Equity Note [Line Items]
Preferred stock, par value | £ / shares								£ 0.05
Stock issued under private placement, value | $					$ 440,108
Estimated offering expense | $		$ 700
Common stock, par value | £ / shares			£ 0.50	£ 0.50				£ 0.50
Series A Preferred Stock
Stockholders Equity Note [Line Items]
American depositary shares conversion rate to preference shares			American Depositary Shares, or ADSs, each representing one share of Amarin’s Series A Convertible Preference Shares
Ordinary Shares
Stockholders Equity Note [Line Items]
Preferred stock, equivalent ordinary shares upon future consolidation outstanding | shares			0	0
Convertible senior notes, total ADS into which the debt is exchangeable | shares				28,931,746		3,886,718	6,283,333
American Depositary Shares | Series A Preferred Stock
Stockholders Equity Note [Line Items]
Issuance of stock (shares) | shares	391,017,970
Stock issued under private placement, value | $	$ 58,600
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