Nature of Business and Basis of Presentation	12 Months Ended
Dec. 31, 2018
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	(1) Nature of Business and Basis of Presentation Nature of Business Amarin Corporation plc (“Amarin” or the “Company”) is a pharmaceutical company with expertise in omega-3 fatty acids and lipid science focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk. The Company’s lead product, Vascepa^® (icosapent ethyl) capsules, is approved by the U.S. Food and Drug Administration, or FDA, for use as an adjunct to diet to reduce triglyceride levels in adult patients with severe (TG ≥500 mg/dL) hypertriglyceridemia. Vascepa is available in the United States by prescription only. In January 2013, the Company began selling and marketing 1-gram size Vascepa capsules in the United States, and in October 2016, introduced a smaller 0.5-gram capsule size. In August 2015, in addition to marketing Vascepa for severe hypertriglyceridemia, the Company commenced marketing Vascepa for use in adult patients with mixed dyslipidemia, as an adjunct to diet and an add-on to statin therapy in patients who despite statin therapy have high triglycerides (TGs ≥200 mg/dL and ≤500 mg/dL), which the Company also refers to as persistently high triglycerides. This expanded promotion of Vascepa commenced pursuant to a federal court order and is continuing pursuant to an agreement among the Company, the FDA and the U.S. government. The Company also developed Vascepa for FDA approval of potential additional indications for use. In particular, the Company conducted a cardiovascular outcomes study of Vascepa, titled REDUCE-IT™ (Reduction of Cardiovascular Events with EPA—Intervention Trial). The REDUCE-IT study, which commenced in 2011 and completed patient enrollment and randomization of 8,179 individual patients in 2016, was designed to evaluate the efficacy of Vascepa in reducing major cardiovascular events in a high-risk patient population on statin therapy. The REDUCE-IT study topline results were made public in September 2018, and the primary results of the REDUCE-IT study were presented at the 2018 Scientific Sessions of the American Heart Association (AHA) in November 2018 with such results concurrently published in The New England Journal of Medicine. The Company sells Vascepa principally to a limited number of major wholesalers, as well as selected regional wholesalers and specialty pharmacy providers, or collectively, its Distributors or its customers, that in turn resell Vascepa to retail pharmacies for subsequent resale to patients and healthcare providers. The Company markets Vascepa in the United States through its direct sales force, which prior to the REDUCE-IT results topline announcement in September 2018 consisted of approximately 170 sales professionals, including sales representatives and their managers, and increased to approximately 440 sales professionals, including approximately 400 sales representatives, to begin 2019. The Company plans to submit an sNDA to the FDA seeking revised labeling for Vascepa based on results of the REDUCE-IT study and, upon such expanded labeling, subject to FDA approval of such label, to further expand its promotion of Vascepa in the United States. Since its commencement in May 2014 until its scheduled expiration on December 31, 2018, Vascepa was co-promoted in the United States under an agreement with Kowa Pharmaceuticals America, Inc. Outside of the United States, the Company has entered into agreements with third party companies in select geographies for purposes of pursuing regulatory approval and commercialization of Vascepa. The Company operates in one business segment. Basis of Presentation The consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (the “U.S.” or the “United States”) and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC. The consolidated financial statements reflect all adjustments of a normal and recurring nature that, in the opinion of management, are necessary to present fairly the Company’s financial position, results of operations and cash flows for the periods indicated. The preparation of the Company’s consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. The results of operations for the years ended December 31, 2018, 2017 and 2016 are not necessarily indicative of the results for any future period. Certain numbers presented throughout this document may not add precisely to the totals provided due to rounding. Absolute and percentage changes are calculated using the underlying amounts in thousands. Certain prior year balances related to beginning and ending cash and cash equivalents and restricted cash in the consolidated statements of cash flows have been conformed to the current year presentation. The accompanying consolidated financial statements of the Company and subsidiaries have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. At December 31, 2018, the Company had current assets of $378.0 million, including cash and cash equivalents of $249.2 million, accounts receivable, net, of $66.5 million and inventory, net, of $57.8 million. The Company’s consolidated balance sheet at December 31, 2018 also includes long-term debt from a royalty-bearing instrument which is anticipated to be repaid quarterly calculated as a percentage of Vascepa net revenues until fully satisfied. As of December 31, 2018, the Company had no other debt outstanding. In January 2017, the Company issued $30.0 million in aggregate principal amount of January 2017 3.5% exchangeable senior notes due 2047, or the 2017 Notes. The terms of the 2017 Notes contained a provision that allowed the Company to elect at its option to cause all or any portion of the 2017 Notes to be mandatorily exchanged into American Depositary Shares (“ADSs”) upon satisfaction of specified equity conditions. In October 2018, the Company exercised that option and mandatorily exchanged the entirety of the 2017 Notes into ADSs resulting in elimination of the debt, such that no amount of 2017 Notes remained as of December 31, 2018. The 2017 Notes were such that they could have been redeemed by the Company for cash on or after January 19, 2021, could have been put back to the Company by the holders on January 19, 2022 for cash equal to 100% of the principal amount plus any accrued and unpaid interest, and could have been exchanged into ADSs at the option of holders at any time after issuance and prior to maturity. Accordingly, the 2017 Notes did not represent a short-term claim on the liquid assets of the Company as of December 31, 2017. The Company believes its cash and cash equivalents will be sufficient to fund its projected operations for at least twelve months and through the likely Prescription Drug User Fee Act (PDUFA) date for approval of a supplemental new drug application (sNDA) by the FDA based on REDUCE-IT study results. Depending on the level of cash generated from operations, and depending in part on the timing and results of the FDA review of the sNDA and rate of prescription growth for Vascepa, additional capital may be required support planned expansion of Vascepa promotion and potential Vascepa promotion beyond which the Company is currently executing. If additional capital is required and the Company is unable to obtain additional capital, the Company may be forced to delay, limit or eliminate certain promotional activities. The Company anticipates that annual net cash outflows in future periods will be variable.

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2018

Nature of Business and Basis of Presentation

(1) Nature of Business and Basis of Presentation

Nature of Business

Amarin Corporation plc (“Amarin” or the “Company”) is a pharmaceutical company with expertise in omega-3 fatty acids and lipid science focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk.

The Company’s lead product, Vascepa^® (icosapent ethyl) capsules, is approved by the U.S. Food and Drug Administration, or FDA, for use as an adjunct to diet to reduce triglyceride levels in adult patients with severe (TG ≥500 mg/dL) hypertriglyceridemia. Vascepa is available in the United States by prescription only. In January 2013, the Company began selling and marketing 1-gram size Vascepa capsules in the United States, and in October 2016, introduced a smaller 0.5-gram capsule size. In August 2015, in addition to marketing Vascepa for severe hypertriglyceridemia, the Company commenced marketing Vascepa for use in adult patients with mixed dyslipidemia, as an adjunct to diet and an add-on to statin therapy in patients who despite statin therapy have high triglycerides (TGs ≥200 mg/dL and ≤500 mg/dL), which the Company also refers to as persistently high triglycerides. This expanded promotion of Vascepa commenced pursuant to a federal court order and is continuing pursuant to an agreement among the Company, the FDA and the U.S. government.

The Company also developed Vascepa for FDA approval of potential additional indications for use. In particular, the Company conducted a cardiovascular outcomes study of Vascepa, titled REDUCE-IT™ (Reduction of Cardiovascular Events with EPA—Intervention Trial). The REDUCE-IT study, which commenced in 2011 and completed patient enrollment and randomization of 8,179 individual patients in 2016, was designed to evaluate the efficacy of Vascepa in reducing major cardiovascular events in a high-risk patient population on statin therapy. The REDUCE-IT study topline results were made public in September 2018, and the primary results of the REDUCE-IT study were presented at the 2018 Scientific Sessions of the American Heart Association (AHA) in November 2018 with such results concurrently published in The New England Journal of Medicine.

The Company sells Vascepa principally to a limited number of major wholesalers, as well as selected regional wholesalers and specialty pharmacy providers, or collectively, its Distributors or its customers, that in turn resell Vascepa to retail pharmacies for subsequent resale to patients and healthcare providers. The Company markets Vascepa in the United States through its direct sales force, which prior to the REDUCE-IT results topline announcement in September 2018 consisted of approximately 170 sales professionals, including sales representatives and their managers, and increased to approximately 440 sales professionals, including approximately 400 sales representatives, to begin 2019. The Company plans to submit an sNDA to the FDA seeking revised labeling for Vascepa based on results of the REDUCE-IT study and, upon such expanded labeling, subject to FDA approval of such label, to further expand its promotion of Vascepa in the United States. Since its commencement in May 2014 until its scheduled expiration on December 31, 2018, Vascepa was co-promoted in the United States under an agreement with Kowa Pharmaceuticals America, Inc. Outside of the United States, the Company has entered into agreements with third party companies in select geographies for purposes of pursuing regulatory approval and commercialization of Vascepa. The Company operates in one business segment.

Basis of Presentation

The consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (the “U.S.” or the “United States”) and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC.

The consolidated financial statements reflect all adjustments of a normal and recurring nature that, in the opinion of management, are necessary to present fairly the Company’s financial position, results of operations and cash flows for the periods indicated. The preparation of the Company’s consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. The results of operations for the years ended December 31, 2018, 2017 and 2016 are not necessarily indicative of the results for any future period. Certain numbers presented throughout this document may not add precisely to the totals provided due to rounding. Absolute and percentage changes are calculated using the underlying amounts in thousands. Certain prior year balances related to beginning and ending cash and cash equivalents and restricted cash in the consolidated statements of cash flows have been conformed to the current year presentation.

The accompanying consolidated financial statements of the Company and subsidiaries have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business.

At December 31, 2018, the Company had current assets of $378.0 million, including cash and cash equivalents of $249.2 million, accounts receivable, net, of $66.5 million and inventory, net, of $57.8 million. The Company’s consolidated balance sheet at December 31, 2018 also includes long-term debt from a royalty-bearing instrument which is anticipated to be repaid quarterly calculated as a percentage of Vascepa net revenues until fully satisfied. As of December 31, 2018, the Company had no other debt outstanding. In January 2017, the Company issued $30.0 million in aggregate principal amount of January 2017 3.5% exchangeable senior notes due 2047, or the 2017 Notes. The terms of the 2017 Notes contained a provision that allowed the Company to elect at its option to cause all or any portion of the 2017 Notes to be mandatorily exchanged into American Depositary Shares (“ADSs”) upon satisfaction of specified equity conditions. In October 2018, the Company exercised that option and mandatorily exchanged the entirety of the 2017 Notes into ADSs resulting in elimination of the debt, such that no amount of 2017 Notes remained as of December 31, 2018. The 2017 Notes were such that they could have been redeemed by the Company for cash on or after January 19, 2021, could have been put back to the Company by the holders on January 19, 2022 for cash equal to 100% of the principal amount plus any accrued and unpaid interest, and could have been exchanged into ADSs at the option of holders at any time after issuance and prior to maturity. Accordingly, the 2017 Notes did not represent a short-term claim on the liquid assets of the Company as of December 31, 2017.

The Company believes its cash and cash equivalents will be sufficient to fund its projected operations for at least twelve months and through the likely Prescription Drug User Fee Act (PDUFA) date for approval of a supplemental new drug application (sNDA) by the FDA based on REDUCE-IT study results. Depending on the level of cash generated from operations, and depending in part on the timing and results of the FDA review of the sNDA and rate of prescription growth for Vascepa, additional capital may be required support planned expansion of Vascepa promotion and potential Vascepa promotion beyond which the Company is currently executing. If additional capital is required and the Company is unable to obtain additional capital, the Company may be forced to delay, limit or eliminate certain promotional activities. The Company anticipates that annual net cash outflows in future periods will be variable.