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Equity - Preferred Stock - Additional Information (Detail) |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 10, 2015 USD ($) $ / shares shares | Mar. 30, 2015 USD ($) | Mar. 05, 2015 USD ($) $ / shares shares | Sep. 30, 2017 USD ($) | Mar. 31, 2015 USD ($) | Sep. 30, 2017 £ / shares shares | Dec. 31, 2015 USD ($) shares | Sep. 30, 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 |  |  |  |  |  |  |
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 |  |  |  |  |  |
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 |  |  |  |
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 |  |  |  |  |  |  |  |  |

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