Amarin (AMRN) 10-Q 5 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	AMRN
Entity Registrant Name	AMARIN CORP PLC\UK
Entity Central Index Key	0000897448
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	000-21392
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	77 Sir John Rogerson’s Quay
Entity Address, Address Line Two	Block C
Entity Address, Address Line Three	Grand Canal Docklands
Entity Address, City or Town	Dublin
Entity Address, Postal Zip Code	2
Entity Address, Country	IE
City Area Code	353 (0) 1
Local Phone Number	6699 020
Document Quarterly Report	true
Document Transition Report	false
Security12b Title	American Depositary Shares (ADS(s)), each ADS representing the right to receive one (1) Ordinary Share of Amarin Corporation plc
Security Exchange Name	NASDAQ
American Depositary Shares
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		388,629,254
Ordinary Shares
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		200,149

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 207,207	$ 644,588
Restricted cash	3,915	3,907
Short-term investments	354,655
Accounts receivable, net	147,292	116,430
Inventory	148,531	76,769
Prepaid and other current assets	26,945	13,311
Total current assets	888,545	855,005
Property, plant and equipment, net	2,166	2,361
Long-term investments	46,092
Operating lease right-of-use asset	8,149	8,511
Other long-term assets	1,074	1,074
Intangible asset, net	14,177	15,258
TOTAL ASSETS	960,203	882,209
Current Liabilities:
Accounts payable	121,366	49,950
Accrued expenses and other current liabilities	189,650	139,826
Debt from royalty-bearing instrument	9,467	50,130
Deferred revenue, current	5,706	2,342
Total current liabilities	326,189	242,248
Long-Term Liabilities:
Deferred revenue, long-term	13,199	18,504
Long-term operating lease liability	9,255	9,443
Other long-term liabilities	4,303	3,751
Total liabilities	352,946	273,946
Commitments and contingencies (Note 6)
Stockholders’ Equity:
Series A Convertible Preferred Stock, £0.05 par, unlimited authorized; 23,850,780 shares issued and outstanding as of September 30, 2020 (equivalent to 2,385,078 ordinary shares upon future consolidation and redesignation at a 10:1 ratio) and 289,317,460 shares issued and outstanding as of December 31, 2019 (equivalent to 28,931,746 ordinary shares upon future consolidation and redesignation at a 10:1 ratio)	5,434	21,850
Common stock, £0.50 par, unlimited authorized; 394,642,079 issued, 388,828,694 outstanding as of September 30, 2020; 365,014,893 issued, 360,103,901 outstanding as of December 31, 2019	287,585	269,173
Additional paid-in capital	1,799,069	1,764,317
Treasury stock; 5,813,385 shares as of September 30, 2020; 4,910,992 shares as of December 31, 2019	(50,728)	(35,900)
Accumulated deficit	(1,434,103)	(1,411,177)
Total stockholders’ equity	607,257	608,263
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 960,203	$ 882,209

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - £ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	£ 0.05	£ 0.05
Preferred stock, shares authorized, unlimited	Unlimited	Unlimited
Preferred stock, issued	23,850,780	289,317,460
Preferred stock, shares outstanding	23,850,780	289,317,460
Preferred stock, equivalent ordinary shares upon future consolidation outstanding	2,385,078	28,931,746
Common stock, par value	£ 0.50	£ 0.50
Common stock, shares authorized, unlimited	Unlimited	Unlimited
Common stock, issued	394,642,079	365,014,893
Common stock, outstanding	388,828,694	360,103,901
Treasury stock, shares	5,813,385	4,910,992

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total revenue, net	$ 156,499	$ 112,408	$ 446,809	$ 286,478
Less: Cost of goods sold	33,071	25,444	96,676	65,354
Gross margin	123,428	86,964	350,133	221,124
Operating expenses:
Selling, general and administrative	120,164	82,559	346,496	227,598
Research and development	10,204	8,923	30,450	23,295
Total operating expenses	130,368	91,482	376,946	250,893
Operating loss	(6,940)	(4,518)	(26,813)	(29,769)
Interest income, net	549	1,146	1,908	238
Other income (expense), net	33	(90)	50	(182)
Loss from operations before taxes	(6,358)	(3,462)	(24,855)	(29,713)
Income tax (provision) benefit	(430)		1,929
Net loss	$ (6,788)	$ (3,462)	$ (22,926)	$ (29,713)
Loss per share:
Basic	$ (0.02)	$ (0.01)	$ (0.06)	$ (0.09)
Diluted	$ (0.02)	$ (0.01)	$ (0.06)	$ (0.09)
Weighted average shares:
Basic	389,699	350,994	378,770	336,938
Diluted	389,699	350,994	378,770	336,938
Product Revenue, Net
Total revenue, net	$ 155,190	$ 112,250	$ 441,118	$ 285,347
Licensing and Royalty Revenue
Total revenue, net	$ 1,309	$ 158	$ 5,691	$ 1,131

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Treasury Shares	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2018	$ 152,330	$ 21,850	$ 246,663	$ (10,413)	$ 1,282,762	$ (1,388,532)
Balance (in shares) at Dec. 31, 2018		289,317,460	329,110,863	(3,260,850)
Exercise of stock options	15,456		$ 2,496		12,960
Exercise of stock options (in shares)			3,838,739
Vesting of restricted stock units	(9,080)		$ 929	$ (9,080)	(929)
Vesting of restricted stock units (in shares)			1,416,124	(526,708)
Stock-based compensation	6,596				6,596
Net income (loss)	(24,431)					(24,431)
Balance at Mar. 31, 2019	140,871	$ 21,850	$ 250,088	$ (19,493)	1,301,389	(1,412,963)
Balance (in shares) at Mar. 31, 2019		289,317,460	334,365,726	(3,787,558)
Balance at Dec. 31, 2018	$ 152,330	$ 21,850	$ 246,663	$ (10,413)	1,282,762	(1,388,532)
Balance (in shares) at Dec. 31, 2018		289,317,460	329,110,863	(3,260,850)
Exercise of stock options (in shares)	5,122,107
Net income (loss)	$ (29,713)
Balance at Sep. 30, 2019	595,896	$ 21,850	$ 266,878	$ (20,533)	1,745,946	(1,418,245)
Balance (in shares) at Sep. 30, 2019		289,317,460	361,368,945	(3,841,615)
Balance at Mar. 31, 2019	140,871	$ 21,850	$ 250,088	$ (19,493)	1,301,389	(1,412,963)
Balance (in shares) at Mar. 31, 2019		289,317,460	334,365,726	(3,787,558)
Issuance of common stock under employee stock purchase plan	837		$ 30		807
Issuance of common stock under employee stock purchase plan (in shares)			47,358
Exercise of stock options	1,888		$ 396		1,492
Exercise of stock options (in shares)			619,404
Vesting of restricted stock units	(1,040)		$ 74	$ (1,040)	(74)
Vesting of restricted stock units (in shares)			116,937	(54,057)
Stock-based compensation	8,351				8,351
Net income (loss)	(1,820)					(1,820)
Balance at Jun. 30, 2019	149,087	$ 21,850	$ 250,588	$ (20,533)	1,311,965	(1,414,783)
Balance (in shares) at Jun. 30, 2019		289,317,460	335,149,425	(3,841,615)
Issuance of common stock, net of transaction costs	440,108		$ 15,879		424,229
Issuance of common stock, net of transaction costs (shares)			25,555,556
Exercise of stock options	2,200		$ 411		1,789
Exercise of stock options (in shares)			663,964
Stock-based compensation	7,963				7,963
Net income (loss)	(3,462)					(3,462)
Balance at Sep. 30, 2019	595,896	$ 21,850	$ 266,878	$ (20,533)	1,745,946	(1,418,245)
Balance (in shares) at Sep. 30, 2019		289,317,460	361,368,945	(3,841,615)
Balance at Dec. 31, 2019	608,263	$ 21,850	$ 269,173	$ (35,900)	1,764,317	(1,411,177)
Balance (in shares) at Dec. 31, 2019		289,317,460	365,014,893	(4,910,992)
Exercise of stock options	1,306		$ 269		1,037
Exercise of stock options (in shares)			412,465
Vesting of restricted stock units	(13,831)		$ 1,274	$ (13,831)	(1,274)
Vesting of restricted stock units (in shares)			1,951,448	(759,832)
Stock-based compensation	10,591				10,591
Net income (loss)	(20,553)					(20,553)
Balance at Mar. 31, 2020	585,776	$ 21,850	$ 270,716	$ (49,731)	1,774,671	(1,431,730)
Balance (in shares) at Mar. 31, 2020		289,317,460	367,378,806	(5,670,824)
Balance at Dec. 31, 2019	$ 608,263	$ 21,850	$ 269,173	$ (35,900)	1,764,317	(1,411,177)
Balance (in shares) at Dec. 31, 2019		289,317,460	365,014,893	(4,910,992)
Exercise of stock options (in shares)	642,756
Net income (loss)	$ (22,926)
Balance at Sep. 30, 2020	607,257	$ 5,434	$ 287,585	$ (50,728)	1,799,069	(1,434,103)
Balance (in shares) at Sep. 30, 2020		23,850,780	394,642,079	(5,813,385)
Balance at Mar. 31, 2020	585,776	$ 21,850	$ 270,716	$ (49,731)	1,774,671	(1,431,730)
Balance (in shares) at Mar. 31, 2020		289,317,460	367,378,806	(5,670,824)
Issuance of common stock under employee stock purchase plan	848		$ 76		772
Issuance of common stock under employee stock purchase plan (in shares)			123,608
Conversion of Series A Convertible Preferred Stock, net	(238)	$ (14,684)	$ 14,684		(238)
Conversion of Series A Convertible Preferred Stock, net (in shares)		(237,713,680)	23,771,368
Exercise of stock options	352		$ 92		260
Exercise of stock options (in shares)			148,290
Vesting of restricted stock units	(521)		$ 104	$ (521)	(104)
Vesting of restricted stock units (in shares)			167,240	(70,971)
Stock-based compensation	12,131				12,131
Net income (loss)	4,415					4,415
Balance at Jun. 30, 2020	602,763	$ 7,166	$ 285,672	$ (50,252)	1,787,492	(1,427,315)
Balance (in shares) at Jun. 30, 2020		51,603,780	391,589,312	(5,741,795)
Conversion of Series A Convertible Preferred Stock, net	(28)	$ (1,732)	$ 1,732		(28)
Conversion of Series A Convertible Preferred Stock, net (in shares)		(27,753,000)	2,775,300
Exercise of stock options	203		$ 53		150
Exercise of stock options (in shares)			82,001
Vesting of restricted stock units	(476)		$ 128	$ (476)	(128)
Vesting of restricted stock units (in shares)			195,466	(71,590)
Stock-based compensation	11,583				11,583
Net income (loss)	(6,788)					(6,788)
Balance at Sep. 30, 2020	$ 607,257	$ 5,434	$ 287,585	$ (50,728)	$ 1,799,069	$ (1,434,103)
Balance (in shares) at Sep. 30, 2020		23,850,780	394,642,079	(5,813,385)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (22,926)	$ (29,713)
Adjustments to reconcile loss to net cash provided by (used in) operating activities:
Depreciation and amortization	446	53
Amortization of investments	771
Stock-based compensation	34,305	22,729
Amortization of debt discount and debt issuance costs	601	1,282
Amortization of intangible asset	1,081	484
Changes in assets and liabilities:
Accounts receivable, net	(30,862)	(37,060)
Inventory	(71,762)	3,245
Prepaid and other current assets	(13,023)	(9,914)
Other long-term assets		(900)
Interest receivable	(1,732)
Accrued interest payable	(348)	(145)
Deferred revenue	(1,941)	(1,131)
Accounts payable and other current liabilities	121,240	54,962
Other long-term liabilities	727	(4,322)
Net cash provided by (used in) operating activities	16,577	(430)
CASH FLOWS FROM INVESTING ACTIVITIES:
Sale and maturities of securities	186,714
Purchases of securities	(587,111)
Purchases of furniture, fixtures and equipment	(252)	(2,114)
Net cash used in investing activities	(400,649)	(2,114)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of transaction costs	848	440,945
Proceeds from exercise of stock options, net of transaction costs	1,861	19,544
Payment of transaction costs for conversion of preferred stock	(266)
Payment on debt from royalty-bearing instrument	(40,916)	(21,441)
Taxes paid related to stock-based awards	(14,828)	(10,120)
Net cash (used in) provided by financing activities	(53,301)	428,928
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	(437,373)	426,384
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, BEGINNING OF PERIOD	648,495	250,727
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH, END OF PERIOD	211,122	677,111
Cash paid during the year for:
Interest	1,882	3,577
Income taxes	$ 197	87
Supplemental disclosure of non-cash transactions:
Initial recognition of operating lease right-of-use asset		$ 8,995

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	(1) Nature of Business and Basis of Presentation Nature of Business Amarin Corporation plc, or Amarin, or the Company, is a pharmaceutical company focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk. The Company’s lead product, VASCEPA ® > ® The Company, since inception, has devoted substantial resources to research and development efforts, most significantly, the development and conduct of REDUCE-IT. The Company announced topline results from REDUCE-IT on September 24, 2018. On November 10, 2018, the Company presented primary results of REDUCE-IT at the 2018 Scientific Sessions of the American Heart Association, or AHA, and the results were concurrently published in The New England Journal of Medicine th Journal of the American College of Cardiology. The FDA granted Priority Review designation to the Company’s March 2019 supplemental new drug application, or sNDA, seeking an expanded indication for VASCEPA in the United States based on the positive results of the REDUCE-IT study. In November 2019, the FDA held an Endocrinologic and Metabolic Drugs Advisory Committee, or EMDAC, meeting to review the REDUCE-IT sNDA. The EMDAC voted unanimously (16-0) to recommend approval of an indication and label expansion for VASCEPA to reduce cardiovascular events in high-risk patients based on the REDUCE-IT results. On December 13, 2019, the FDA approved a new indication and related label expansion based on REDUCE-IT. Reflecting the robust results of the clinical development program for VASCEPA, no additional post-approval clinical study or other special post-approval requirement (as often seen with other drug approvals) was requested by the FDA in conjunction with its approval of VASCEPA. In the United States, 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. Prior to the REDUCE-IT results topline announcement in September 2018, the Company’s commercialization of VASCEPA was somewhat limited. Subsequent to learning the positive cardiovascular outcomes results of the REDUCE-IT study, the Company increased its promotional efforts. Based on the positive REDUCE-IT results, in early 2019, the Company increased the size of its direct sales force to approximately 440 sales professionals, including approximately 400 sales representatives. As a result of the FDA’s approved indication and label expansion in December 2019, in early 2020 the Company completed the expansion of its direct sales force to approximately 900 sales professionals, including approximately 800 sales representatives. In addition to promotion of VASCEPA in the United States, based on REDUCE-IT, the Company has increased focus on expansion of the Company’s development efforts for VASCEPA to major markets outside the United States. The Company currently has strategic collaborations to develop and commercialize VASCEPA in select territories outside the United States. The Company operates in one business segment. On March 30, 2020, the United States District Court for the District of Nevada, or the Nevada Court, ruled in favor of two generics companies in Amarin’s patent litigation related to its abbreviated new drug applications, or ANDAs, that seek FDA approval for sale of generic versions of VASCEPA for the original indication of VASCEPA as an adjunct to diet to reduce triglyceride, or TG, levels in adult patients with severe ( > 500 mg/dL) hypertriglyceridemia. On May 22, 2020 and August 10, 2020, the two generics companies, Hikma Pharmaceutical USA Inc., or Hikma, and Dr. Reddy’s Laboratories, Inc., or Dr. Reddy’s, respectively, received FDA approval to market its generic versions of VASCEPA. On September 3, 2020, the U.S. Court of Appeals for the Federal Circuit, or the Federal Circuit, upheld the March ruling by the Nevada Court in favor of the two generics companies. On October 2, 2020, the Company filed a combined petition for panel rehearing or rehearing en banc . On November 4, 2020, our rehearing and en banc petitions were denied. Amarin plans to file a writ of certiorari within 90 days of such denial to ask the United States Supreme Court to hear our appeal. Amarin intends to vigorously pursue this matter, but cannot predict the outcome. To date, Hikma and Dr. Reddy’s have not launched generic versions of VASCEPA, although, following the outcome of the appeal trial on September 3, 2020, Hikma announced it is working towards a launch. Geographies outside the United States in which VASCEPA is sold and under regulatory review are not subject to this U.S. patent litigation and judgment. No similar litigation involving potential generic versions of VASCEPA is pending outside the United States. VASCEPA is currently available by prescription in Canada, Lebanon and the United Arab Emirates. In Canada, VASCEPA has the benefit of eight years of data protection afforded through Health Canada (until the end of 2027), in addition to separate patent protection with expiration dates that could extend into 2039. Amarin is pursuing additional regulatory approvals for VASCEPA in Europe, China and the Middle East. In China and the Middle East, Amarin is pursuing such regulatory approvals and subsequent commercialization of VASCEPA with commercial partners. In Europe, ten to eleven years of market protection is anticipated due to regulatory exclusivity in the European Union subject to an approval recommendation by the EMA and associated EC approval, in addition to pending patent protection that could extend into 2039. Amarin is responsible for supplying VASCEPA to all markets in which the product is sold, including in Canada, China, Lebanon and the United Arab Emirates where the drug is promoted and sold via collaboration with third-party companies that compensate Amarin for such supply. We are not responsible for providing any generic company with drug product. Basis of Presentation The condensed consolidated financial statements included herein have been prepared by the Company, without audit, in accordance with accounting principles generally accepted in the United States and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC. Certain information in the footnote disclosures of the financial statements has been condensed or omitted where it substantially duplicates information provided in the Company’s latest audited consolidated financial statements, in accordance with the rules and regulations of the SEC. These condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and notes included in its Annual Report on Form 10-K for the fiscal year ended December 31, 2019, or the 2019 Form 10-K, filed with the SEC. The balance sheet amounts at December 31, 2019 in this report were derived from the Company’s audited 2019 consolidated financial statements included in the 2019 Form 10-K. The condensed 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 condensed consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles, or 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 three and nine months ended September 30, 2020 are not necessarily indicative of the results for the entire fiscal year or 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. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying condensed 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, as well as the current global pandemic, COVID-19. As of September 30, 2020, the Company had Total assets of $960.2 million, of which $608.0 million consisted of cash and liquid short-term and long-term investments. More specifically, the Company had Current assets of $888.5 million, including Cash and cash equivalents of $207.2 million, Short-term investments of $354.7 million, Accounts receivable, net, of $147.3 million and Inventory of $148.5 million. In addition, as of September 30, 2020, the Company has Long-term investments of $46.1 million. The Company’s condensed consolidated balance sheets also include a $9.5 million liability under its royalty-bearing instrument which amount, when paid during the fourth quarter of 2020, will be the final payment under such instrument and an end to the quarterly installments calculated as 10 % of quarterly VASCEPA net revenues which the Company has incurred since the product was launched in 2013. As of September 30, 2020 , the Company had no other debt outstanding.

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	(2) Significant Accounting Policies Revenue Recognition In accordance with Accounting Standards Codification, or ASC, Topic 606, Revenue from Contracts with Customers Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of purchase of 90 days or less. Restricted cash represents cash and cash equivalents pledged to guarantee repayment of certain expenses which may be incurred for business travel under corporate credit cards held by employees. Accounts Receivable, net Accounts receivable, net, comprised of trade receivables, are generally due within 30 days and are stated at amounts due from customers. The Company recognizes an allowance for losses on accounts receivable in an amount equal to the estimated probable losses net of any recoveries. The allowance is based primarily on assessment of specific identifiable customer accounts considered at risk or uncollectible, as well as an analysis of current receivables aging and expected future write-offs. The expense associated with the allowance for doubtful accounts is recognized as Selling, general, and administrative expense. The Company has not historically experienced any significant credit losses. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2020 and December 31, 2019: In thousands September 30, 2020 December 31, 2019 Gross trade accounts receivable $ 223,579 $ 149,567 Trade allowances (63,069 ) (29,261 ) Chargebacks (12,273 ) (3,876 ) Allowance for doubtful accounts (945 ) — Accounts receivable, net $ 147,292 $ 116,430 Inventory The Company states inventories at the lower of cost or net realizable value. Cost is determined based on actual cost using the average cost method. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. An allowance is established when management determines that certain inventories may not be saleable. If inventory cost exceeds expected net realizable value due to obsolescence, damage or quantities in excess of expected demand, changes in price levels or other causes, the Company will reduce the carrying value of such inventory to net realizable value and recognize the difference as a component of cost of goods sold in the period in which it occurs. The Company capitalizes inventory purchases of saleable product from approved suppliers while inventory purchases from suppliers prior to regulatory approval are included as a component of research and development expense. The Company expenses inventory identified for use as marketing samples when they are packaged. The average cost reflects the actual purchase price of VASCEPA active pharmaceutical ingredient, or API. Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences of differences between the carrying amounts and tax bases of assets and liabilities and operating loss carryforwards and other tax attributes using enacted rates expected to be in effect when those differences reverse. Valuation allowances are provided against deferred tax assets that are not more likely than not to be realized. Deferred tax assets and liabilities are classified as non-current in the condensed consolidated balance sheet. The Company provides reserves for potential payments of tax to various tax authorities and does not recognize tax benefits related to uncertain tax positions and other issues. Tax benefits for uncertain tax positions are based on a determination of whether a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized, assuming that the matter in question will be decided based on its technical merits. The Company’s policy is to record interest and penalties in the income tax provision, as applicable. The Company regularly assesses its ability to realize deferred tax assets. Changes in historical earnings performance, future earnings projections, and changes in tax laws, among other factors, may cause the Company to adjust its valuation allowance on deferred tax assets, which would impact the Company’s income tax expense in the period in which it is determined that these factors have changed. Excess tax benefits and deficiencies that arise upon vesting or exercise of share-based payments are recognized as an income tax benefit and expense, respectively, in the condensed consolidated statement of operations. Excess income tax benefits are classified as cash flows from operating activities and cash paid to taxing authorities arising from the withholding of shares from employees are classified as cash flows from financing activities. The Company’s and its subsidiaries’ income tax returns are periodically examined by various tax authorities, including the Internal Revenue Service, or IRS, and states. The IRS began an examination of the Company’s 2018 U.S. income tax return in the first quarter of 2020. Although the outcome of tax audits is always uncertain and could result in significant cash tax payments, the Company does not believe the outcome of this audit will have a material adverse effect on its consolidated financial position or results of operations. Loss per Share Basic net loss per share is determined by dividing net loss by the weighted average shares of common stock outstanding during the period. Diluted net loss per share is determined by dividing net loss by diluted weighted average shares outstanding. Diluted weighted average shares outstanding reflects the dilutive effect, if any, of potentially dilutive common shares, such as common stock options calculated using the treasury stock method and convertible preferred stock using the “if-converted” method. In periods with reported net operating losses, all common stock options are deemed anti-dilutive such that basic net loss per share and diluted net loss per share are equal. The Company’s preferred stock is entitled to receive dividends on an as-if-converted basis in the same form as dividends actually paid on common shares. Accordingly, the preferred stock is considered a participating security and the Company is required to apply the two-class method to consider the impact of the preferred stock on the calculation of basic and diluted earnings per share. The Company is in a net loss position for all periods presented and is therefore not required to present the two-class method, however, in the event the Company is in a net income position, the two-class method must be applied for this period by allocating all earnings during the period to common shares and preferred stock based on their contractual entitlements assuming all earnings are distributed. The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2020 and 2019 are as follows: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Net loss—basic and diluted $ (6,788 ) $ (3,462 ) $ (22,926 ) $ (29,713 ) Weighted average shares outstanding—basic and diluted 389,699 350,994 378,770 336,938 Net loss per share—basic and diluted $ (0.02 ) $ (0.01 ) $ (0.06 ) $ (0.09 ) For the three and nine months ended September 30, 2020 and 2019, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Stock options 17,479 16,259 17,479 16,259 Restricted stock and restricted stock units 7,727 9,359 7,727 9,359 Preferred stock, if converted 2,385 28,932 2,385 28,932 Stock options are anti-dilutive during periods of net earnings when the exercise price of the stock options exceeds the market price of the underlying shares on the last day of the reporting period. Restricted stock and restricted stock units are anti-dilutive during periods of net earnings when underlying performance-based vesting requirements were not achieved as of the last day of the reporting period. Concentration of Credit Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents, short-term and long-term investments, and accounts receivable. The Company maintains substantially all of its cash and cash equivalents, and short-term and long-term investments, in financial institutions believed to be of high-credit quality. A significant portion of the Company’s sales are to wholesalers in the pharmaceutical industry. The Company monitors the creditworthiness of customers to whom it grants credit terms and has not experienced any credit losses. The Company does not require collateral or any other security to support credit sales. Three customers individually accounted for 10% or more of the Company’s gross product sales. Customers A, B, and C accounted for 25%, 37%, and 30%, respectively, of gross product sales for the nine months ended September 30, 2020, and represented 37%, 32%, and 25%, respectively, of the gross accounts receivable balance as of September 30, 2020. Customers A, B, and C accounted for 25%, 36%, and 29%, respectively, of gross product sales for the nine months ended September 30, 2019 and represented 42%, 23%, and 28%, respectively, of the gross accounts receivable balance as of September 30, 2019. The Company has not experienced any significant write-offs of its accounts receivable. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. Concentration of Suppliers The Company has contractual freedom to source the API for VASCEPA and to procure other services supporting its supply chain and has entered into supply agreements with multiple suppliers. The Company’s supply of product for commercial sale and clinical trials is dependent upon relationships with third-party manufacturers and suppliers. The Company cannot provide assurance that its efforts to procure uninterrupted supply of VASCEPA to meet market demand will continue to be successful or that it will be able to renew current supply agreements on favorable terms or at all. Significant alteration to or disruption or termination of the Company’s current supply chain, including as a result of COVID-19, or the Company’s failure to enter into new and similar agreements in a timely fashion, if needed, could have a material adverse effect on its business, condition (financial and other), prospects or results of operations. The Company currently has manufacturing agreements with multiple independent FDA-approved API manufacturers and several independent FDA-approved API encapsulators and packagers for VASCEPA manufacturing. Each of these companies has qualified and validated its manufacturing processes and is capable of manufacturing VASCEPA. There can be no guarantee that these or other suppliers with which the Company may contract in the future to manufacture VASCEPA or VASCEPA API will remain qualified to do so to the Company’s specifications or that these and any future suppliers will have the manufacturing capacity to meet anticipated demand for VASCEPA. Fair Value of Financial Instruments The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data. The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2020 and December 31, 2019 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 81,714 $ 81,714 $ — $ — U.S. Treasury Shares 59,959 59,959 — — Corporate Bonds 200,704 — 200,704 — Commercial Paper 110,858 — 110,858 — Agency Securities 14,027 — 14,027 — Repo Securities 11,000 — 11,000 — Asset Backed Securities 8,887 — 8,887 — Certificate of Deposit 6,129 — 6,129 — Total $ 493,278 $ 141,673 351,605 $ — December 31, 2019 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 10,078 $ 10,078 $ — $ — The carrying amount of the Company’s cash and cash equivalents approximates fair value because of their short-term nature. The cash and cash equivalents consists of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of the purchase of 90 days or less. The Company’s held-to-maturity investments are stated at amortized cost, which approximates fair value. The Company does not intend to sell these investment securities and the contractual maturities are not greater than 24 months. Those with maturities greater than 90 days and less than twelve months are included in short-term investments on its condensed consolidated balance sheet. Those with remaining maturities in excess of twelve months are included in long-term investments on its condensed consolidated balance sheet. Unrealized gains or losses on held-to-maturity securities are not recognized until maturity, except other-than-temporary unrealized losses which are recognized in earnings in the period incurred. The Company evaluates securities with unrealized losses to determine whether such losses are other than temporary. Interest on investments is reported in interest income. The unrealized gain for the nine months ended September 30, 2020 and 2019 was $0.9 million and nil, respectively. The carrying amounts of accounts payable and accrued liabilities approximate fair value because of their short-term nature. The carrying amounts and the estimated fair values of debt from royalty-bearing instrument as of September 30, 2020 and December 31, 2019 are as follows: September 30, 2020 December 31, 2019 In thousands Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Debt from royalty-bearing instrument $ 9,387 $ 9,500 $ 49,702 $ 50,400 The estimated fair value of the debt from royalty-bearing instrument is calculated utilizing the same Level 3 inputs utilized in valuing the related derivative liability (see Derivative Liabilities below). The carrying value of the debt from royalty-bearing instrument is net of the unamortized debt discounts and issuance costs as of both September 30, 2020 and December 31, 2019. The carrying value of the debt from the royalty-bearing instrument as of September 30, 2020 approximates fair value because the instrument will be paid in full in the fourth quarter of 2020. Derivative Liabilities Derivative financial liabilities are recorded at fair value, with gains and losses arising for changes in fair value recognized in the condensed consolidated statement of operations at each period end while such instruments are outstanding. If the Company issues shares to discharge the liability, the derivative financial liability is derecognized and common stock and additional paid-in capital are recognized on the issuance of those shares. Long-Term Debt Redemption Feature The Company’s December 2012 royalty-bearing instrument financing arrangement (discussed in Note 5—Debt) is scheduled to be fully repaid in the fourth quarter of 2020. Accounting for this instrument since its inception in 2012 has included reporting of an embedded derivative reflect contains a redemption feature whereby, upon a change of control, the Company would be required to repay $150.0 million, less any previously repaid amount. The Company determined this redemption feature to be an embedded derivative, which is carried at fair value and is classified as Level 3 in the fair value hierarchy due to the use of significant unobservable inputs. The fair value of the embedded derivative was calculated using a probability-weighted model incorporating management estimates of future revenues and for a potential change in control, and by determining the fair value of the debt with and without the change in control provision included. The difference between the two was determined to be the fair value of the embedded derivative. The fair value of this derivative liability is remeasured at each reporting period, with changes in fair value recognized in the condensed consolidated statement of operations. As of September 30, 2020, the fair value of the derivative was determined to be nil, and the debt was valued by comparing debt issues of similar companies with (i) remaining terms of between 1.2 and 6.5 years, (ii) coupon rates of between 6.0% and 11.5% and (iii) market yields of between 5.4% and 16.4%. As of December 31, 2019, the fair value of the derivative was determined to be nil based on underlying assumptions, and the debt was valued by comparing debt issues of similar companies with (i) remaining terms of between 1.9 and 7.3 years, (ii) coupon rates of between 6.0% and 11.5% and (iii) market yields of between 5.2% and 16.8%. As such, the Company recognized no gain or loss on change in fair value of derivative liability for the nine months ended September 30, 2020 and 2019. Certain changes in the assumptions used to value the derivative liability, including the probability of a change in control, could potentially result in a change to the carrying value of such liability. Because the remaining amount due from this royalty-bearing instrument is fixed and will be fully paid in the fourth quarter of 2020, any change in the value of this derivative liability will not have any impact on the Company’s aggregate cash payment obligation from this instrument regardless of any potential change in the carrying value of such liability. Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated on a regular basis by the chief operating decision-maker, or decision-making group, in deciding how to allocate resources to an individual segment and in assessing performance of the segment. The Company currently operates in one business segment, which is the development and commercialization of VASCEPA. A single management team that reports to the Company’s chief decision-maker, who is the Chief Executive Officer, comprehensively manages the business. Accordingly, the Company does not have separately reportable segments. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, and are early adopted by the Company or adopted as of the specified effective date. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808), Clarifying the Interaction between Topic 808 and Topic 606, which clarified that in collaborative arrangements where the counterparty is a customer for a good or service that is a distinct unit of account is required to be accounted for under ASC 606. The Company adopted this standard effective January 1, 2020, which did not have an impact on the Company’s condensed consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, which requires earlier recognition of credit losses on loans and other financial instruments held by entities, including trade receivables. The new standard requires entities to measure all expected credit losses for financial assets held at each reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The Company adopted this standard effective January 1, 2020, which did not have a material impact on the Company’s condensed consolidated financial statements. The Company also considered the following recent accounting pronouncement which was not yet adopted as of September 30, 2020: In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, the recognition of deferred tax liabilities for outside basis differences, among other simplifications. The new guidance is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early adoption of all amendments in the same period is permitted. The Company is currently evaluating the impact that this standard will have on the Company’s condensed consolidated financial statements. The Company believes that the impact of other recently issued but not yet adopted accounting pronouncements will not have a material impact on the Company’s condensed consolidated financial position, results of operations, and cash flows, or do not apply to the Company’s operations.

Intangible Asset

Intangible Asset	9 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Asset	(3) Intangible Asset Intangible asset consists of the historical acquisition cost of certain technology rights for VASCEPA. Upon approval by FDA on December 13, 2019 of a new indication of VASCEPA, a milestone for £5 million was achieved, which resulted in the Intangible asset increasing by $8.5 million. The Intangible asset has an estimated weighted-average remaining useful life of 9.8 years. The carrying value as of September 30, 2020 and December 31, 2019 is as follows: In thousands September 30, 2020 December 31, 2019 Technology rights $ 20,081 $ 20,081 Accumulated amortization (5,904 ) (4,823 ) Intangible asset, net $ 14,177 $ 15,258

Inventory

Inventory	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventory	(4) Inventory The Company capitalizes its purchases of saleable inventory of VASCEPA from suppliers that have been qualified by the FDA. Inventories as of September 30, 2020 and December 31, 2019 consist of the following: In thousands September 30, 2020 December 31, 2019 Raw materials $ 32,956 $ 19,455 Work in process 23,386 12,031 Finished goods 92,189 45,283 Total inventory $ 148,531 $ 76,769

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	(5) Debt Long-Term Debt from Royalty-Bearing Instrument—December 2012 Financing On December 6, 2012, the Company entered into a Purchase and Sale Agreement with BioPharma Secured Debt Fund II Holdings Cayman LP, or BioPharma. Under this agreement, the Company granted to BioPharma a security interest in future receivables associated with the VASCEPA patent rights, in exchange for $100.0 million received at the closing of the agreement which occurred in December 2012. Under these terms, the Company continues to own all VASCEPA intellectual property rights, however, such rights, as described below, could be used as collateral for repayment of the remaining unpaid balance under this agreement if the Company defaults on making required payments. In the agreement, the Company agreed to repay BioPharma up to $150.0 million with such repayment based on a portion of net revenues and receivables generated from VASCEPA. On December 20, 2017, BioPharma assigned all rights under this agreement to CPPIB Credit Europe S.à r.l., or CPPIB. As of September 30, 2020, the remaining amount to be repaid to CPPIB is $9.6 million, which includes $0.1 million of interest. During the three and nine months ended September 30, 2020 , the Company made repayments under the agreement of $13.4 million and $42.8 million, respectively, to CPPIB and the remaining $9.6 million is scheduled to be paid in November 2020 for the third quarter of 2020, which will be the final payment on the debt. Previously, these payments, were calculated as 10% of VASCEPA net product revenues. All such payments reduced the remainder of the $150.0 million in aggregate payments to CPPIB. Except upon a change of control in Amarin, the agreement does not expire until $150.0 million in aggregate has been repaid, which will be fully repaid during the fourth quarter of 2020. The Company determined the redemption feature upon a change of control to be an embedded derivative requiring bifurcation. The fair value of the embedded derivative was calculated by determining the fair value of the debt with the change in control provision included and also without the change in control provision. The fair value of this derivative liability is remeasured at each reporting period, with changes in fair value recognized in the condensed consolidated statement of operations and any changes in the assumptions used in measuring the fair value of the derivative liability could result in a material increase or decrease in its carrying value. Based on current assumptions underlying the valuation, the Company recognized no gain or loss on change in fair value of derivative liability during the nine months ended September 30, 2020 and 2019. As of September 30, 2020 and December 31, 2019, the carrying value of the royalty-bearing instrument, net of the unamortized debt discount and issuance costs, was $9.4 million and $49.7 million, respectively. During the nine months ended September 30, 2020, the Company recorded cash and non-cash interest expense of $1.5 million and $0.6 million, respectively, in connection with the royalty-bearing instrument. During the nine months ended September 30, 2019, the Company recorded $3.4 million and $1.3 million of cash and non-cash interest expense, respectively, in connection with the royalty-bearing instrument. The Company will periodically evaluate the remaining term of the agreement and the effective interest rate is recalculated each period based on the Company’s most current estimate of repayment. To secure the obligations under the agreement, the Company granted BioPharma, which it subsequently assigned to CPPIB, a security interest in the Company’s patents, trademarks, trade names, domain names, copyrights, know-how and regulatory approvals related to the covered products, all books and records relating to the foregoing and all proceeds of the foregoing, referred to collectively as the collateral. If the Company (i) fails to deliver a payment when due and does not remedy that failure within a specific notice period, (ii) fails to maintain a first-priority perfected security interest in the collateral in the United States and does not remedy that failure after receiving notice of such failure or (iii) becomes subject to an event of bankruptcy, then CPPIB may attempt to collect the maximum amount payable by the Company under this agreement (after deducting any payments the Company has already made). Under the agreement, the Company is restricted from paying dividends on its common shares, unless it has cash and cash equivalents in excess of a specified amount after such payment.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	(6) Commitments and Contingencies Litigation In the ordinary course of business, the Company is from time to time involved in lawsuits, claims, investigations, proceedings, and threats of litigation relating to intellectual property, commercial arrangements and other matters. Refer to Item 1 Legal Proceedings of this Quarterly Report on Form 10-Q below for a discussion of the Company’s current legal proceedings. Milestone and Supply Purchase Obligations The Company entered into long-term supply agreements with multiple FDA-approved API suppliers and encapsulators. Certain supply agreements require annual minimum volume commitments by the Company and certain volume shortfalls may require payments for such shortfalls. These agreements include requirements for the suppliers to meet certain product specifications and qualify their materials and facilities with applicable regulatory authorities including the FDA. The Company has incurred certain costs associated with the qualification of product produced by these suppliers. Pursuant to the supply agreements, there is a total of approximately $164.7 million that is potentially payable over the term of such agreements based on minimum purchase obligations. The Company continues to meet its contractual purchase obligations. Under the 2004 share repurchase agreement with Laxdale Limited or Laxdale, upon receipt of marketing approval in Europe for the first indication for VASCEPA (or first indication of any product containing Amarin Neuroscience Limited intellectual property acquired from Laxdale in 2004), the Company must make an aggregate stock or cash payment to the former shareholders of Laxdale (at the sole option of each of the sellers) of £7.5 million (approximately $9.7 million as of September 30, 2020). Also under the Laxdale agreement, upon receipt of a marketing approval in Europe for a further indication of VASCEPA (or further indication of any other product using Amarin Neuroscience Limited intellectual property), the Company must make an aggregate stock or cash payment (at the sole option of each of the sellers) of £ 5 million (approximately $6.4 million as of September 30, 2020 ) for the potential market approval. The Company has no provision for any of the obligations above since the amounts are either not paid or payable as of September 30, 2020.

Equity

Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Equity	(7) Equity Preferred Stock On March 5, 2015, the Company entered into a subscription agreement with four institutional investors, or the Purchasers, including both existing and new investors, for the private placement of 352,150,790 restricted American Depositary Shares, each representing one (1) share of Amarin’s Series A Convertible Preference Shares, par value £0.05 per share, in the capital of the Company, or Series A Preference Shares, resulting in gross proceeds to the Company of $52.8 million. The closing of the private placement occurred on March 30, 2015. For each restricted American Depositary Share, the Purchasers paid a negotiated price of $0.15 (equating to $1.50 on an as-if-converted-to-ordinary-shares basis), resulting in $52.8 million in aggregate gross proceeds to the Company, before deducting estimated offering expenses of approximately $0.7 million. The net proceeds are reflected as preferred stock in the accompanying condensed consolidated balance sheets. Each ten (10) Series A Preference Shares may be consolidated and redesignated as one (1) ordinary share, par value £0.50 per share, in the capital of the Company, each ordinary share to be represented by American Depositary Shares, or ADSs, provided that consolidation will be prohibited if, as a result, the holder of such Series A Preference Shares and its affiliates would beneficially own more than 9.9% (increased from 4.99% effective March 2020) of the total number of Amarin ordinary shares or ADSs outstanding following such redesignation, or the Beneficial Ownership Limitation. By written notice to the Company, a holder may from time to time increase or decrease the Beneficial Ownership Limitation to any other percentage not in excess of 19.9% specified in such notice; provided that any such increase will not be effective until the sixty-first (61st) day after such notice is delivered to the Company. This consolidation and redesignation may be effected by a holder of Series A Preference Shares following the first to occur of the resale of the ADSs representing the ordinary shares being registered for resale under the Securities Act pursuant to an effective registration statement, following any sale of the ADSs representing the ordinary shares pursuant to Rule 144 under the Securities Act, or if such ADSs representing the ordinary shares are eligible for sale under Rule 144, following the expiration of the one-year holding requirement under Rule 144. Except as otherwise provided in the Series A Preference Share Terms or as required by applicable law, the Series A Preference Shares have no voting rights. However, as long as any Series A Preference Shares are outstanding, the Company cannot, without the approval of the holders of seventy-five percent (75%) of the then outstanding Series A Preference Shares, alter or change adversely the powers, preferences or rights attaching to the Series A Preference Shares or enter into any agreement with respect to the foregoing. Holders of the Series A Preference Shares are entitled to receive, and the Company is required to pay, dividends (other than dividends in the form of ordinary shares) on the Series A Preference Shares equal (on an as-if-converted-to-ordinary-shares basis) to and in the same form as dividends (other than dividends in the form of ordinary shares) actually paid on ordinary shares when, as and if such dividends (other than dividends in the form of ordinary shares) are paid on the ordinary shares. The restricted American Depositary Shares and Series A Preference Shares were sold in a transaction exempt from the registration requirements under the Securities Act of 1933, as amended, or the Securities Act. The Company filed a registration statement with the SEC covering the resale of the restricted American Depositary Shares and the ADSs representing ordinary shares created by the consolidation and redesignation of the Series A Preference Shares, or the Registrable Securities, on April 9, 2015, which was declared effective by the SEC on May 1, 2015. In addition, the Company agreed to use its commercially reasonable best efforts to keep the registration, and any qualification, exemption or compliance under state securities laws which the Company determines to obtain, continuously effective, and to keep the Registration Statement free of any material misstatements or omissions, until the earlier of (a) March 11, 2017 or (b) the date on which all Registrable Securities held by Purchasers may be sold or transferred in compliance with Rule 144 under the Securities Act, without any volume or manner of sale restrictions. During April 2020, at the request of certain holders, 237,713,680 Series A Preference Shares were consolidated and redesignated, resulting in the issuance of 23,771,368 ordinary shares. During July 2020, at the request of certain holders, 27,753,000 Series A Preference Shares were consolidated and redesignated, resulting in the issuance of 2,775,300 ordinary shares. As of September 30, 2020, a total of 328,300,010 Series A Preference Shares had been consolidated and redesignated at the request of holders, resulting in the issuance of 32,830,001 ADSs, such that a maximum of 2,385,078 ordinary shares remained issuable upon future consolidation and redesignation of the remaining Series A Preference Shares as of September 30, 2020, subject to certain adjustments for dilutive events. Common Stock On March 16, 2020, the Company’s Board of Directors, upon the recommendation of the Remuneration Committee and based on input from Radford, part of the Rewards Solutions practice of Aon Plc, as independent external compensation consultants to the Company’s Remuneration Committee, adopted, subject to shareholder approval, the Amarin Corporation plc 2020 Stock Incentive Plan, or the 2020 Plan, which was subsequently approved by the Company’s shareholders on July 13, 2020 at the Annual General Meeting of Shareholders. The 2020 Plan is the successor to the Amarin Corporation plc 2011 Stock Option Plan, as amended, or the 2011 Plan, which expired on July 12, 2021. The maximum number of the Company’s ordinary shares of £0.50 each or equivalent ADSs to be issued under the 2020 Plan shall not exceed the sum of (i) 20,000,000 shares and (ii) the number of shares that remained available for grant under the 2011 Plan as of the date the 2020 Plan was approved by the Company’s shareholders. The number of shares remaining under the 2011 Plan was approximately 2,634,440. The award of stock options (both incentive and non-qualified stock options), restricted stock units, and certain limited unrestricted share awards are permitted. The 2020 Plan is administered by the Remuneration Committee of the Board of Directors and will expire on July 13, 2030. During the nine months ended September 30, 2020 and 2019, in addition to ordinary shares issued as described in Preferred Stock Incentive Equity Awards On July 18, 2019, the Company completed a public offering of 22,222,223 ADSs with each ADS representing one ordinary share of the Company, at a price of $18.00 per ADS after commission. In addition, the Company granted the underwriters a 30-day option to purchase up to an additional 3,333,333 ADSs at a price of $18.00 per ADS. On July 29, 2019, the underwriters exercised the full option. This public offering, including the exercised option, resulted in gross proceeds of approximately $460.0 million and, after deducting customary commissions and offering expenses, net proceeds to the Company of approximately $440.1 million. Incentive Equity Awards As of September 30, 2020, there were an aggregate of 17,478,906 stock options and 7,727,158 restricted stock units, or RSUs, outstanding under the 2020 Plan representing approximately 4% and 2%, respectively, of outstanding shares (including common and preferred shares) on a fully diluted basis. During the nine months ended September 30, 2020 and 2019, the Company issued 642,756 and 5,122,107 common shares, respectively, as a result of the exercise of stock options, resulting in gross and net proceeds of $1.9 million during the nine months ended September 30, 2020 and $19.5 million during the nine months ended September 30, 2019. During the nine months ended September 30, 2020 and 2019, the Company issued 1,206,494 and 1,533,061 common shares, respectively, related to the vesting of RSUs, of which 440,573 and 580,765 shares, respectively, were retained as treasury shares as settlement of employee tax obligations. Of these shares issued during the nine months ended September 30, 2020, in connection with the achievement of certain regulatory and sales performance conditions associated with the REDUCE-IT clinical trial and subsequent revenue growth, the Company issued 1,107,660 common shares upon vesting of performance-based RSUs granted in 2017 and 2018, of which 461,820 shares were retained as treasury shares as settlement of employee tax obligations. These performance-based RSUs will continue to vest ratably monthly through August 2021. On July 13, 2020, the Company granted a total of 164,657 RSUs and 210,764 stock options to members of the Company’s Board of Directors under the 2020 Plan. The RSUs vest in equal installments over a three-year On July 1, 2020, the Company granted 100,000 RSUs to employees under the 2011 Plan that vest upon the achievement of specified sales performance conditions. On June 1, 2020, the Company granted a total of 782,520 RSUs to employees under the 2011 Plan. The RSUs vest quarterly over a three-year On March 2, 2020 and February 3, 2020, the Company granted a total of 821,950 RSUs and 1,875,000 stock options, respectively, to employees under the 2011 Plan. The RSUs vest annually over a three-year four-year On May 20, 2019, the Company granted a total of 45,163 RSUs and 58,721 stock options to members of the Company’s Board of Directors under the 2011 Plan. The RSUs vest in equal installments over a three-year Also on May 20, 2019, the Company granted an additional 20,000 RSUs to employees under the 2011 Plan that vest upon the achievement of a specified sales performance condition. On February 1, 2019, the Company granted a total of 757,800 RSUs and 1,193,400 stock options to employees under the 2011 Plan. The RSUs vest annually over a three-year four-year

Co-Promotion Agreement

Co-Promotion Agreement	9 Months Ended
	Sep. 30, 2020
Co Promotion Agreement [Abstract]
Co-Promotion Agreement	(8) Co-Promotion Agreement On March 31, 2014, the Company entered into a Co-Promotion Agreement, or the Agreement, with Kowa Pharmaceuticals America, Inc. related to the commercialization of VASCEPA capsules in the United States. The Co-Promotion Agreement, as amended in 2017, intentionally designed the co-promotion to naturally end as of December 31, 2018 and the companies mutually agreed not to renew the agreement. During 2018, which was the last year of co-promotion of VASCEPA by Kowa Pharmaceuticals America, Inc., the Company incurred expense for co-promotion tail payments which are calculated as a percentage of the 2018 co-promotion fee, which was eighteen and a half percent (18.5%) of VASCEPA gross margin in 2018. The accrued tail payments are paid over three years with declining amounts each year. Kowa Pharmaceuticals America, Inc. was eligible to receive $17.8 million in co-promotion tail payments, the present value of which $16.6 million, was fully accrued as of December 31, 2018. As of September 30, 2020 and December 31, 2019, a net payable to Kowa Pharmaceuticals America, Inc. of $5.2 million and $10.0 million, respectively, of which $3.9 million and $6.5 million, respectively, was classified as current on the condensed consolidated balance sheets, representing the remaining accrued co-promotion tail payments

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Revenue Recognition	(9) Revenue Recognition The Company sells VASCEPA principally to a limited number of major wholesalers, as well as selected regional wholesalers and specialty pharmacy providers in the United States, or collectively, its distributors or its customers, that in turn resell VASCEPA to retail pharmacies for subsequent resale to patients and healthcare providers. Patients are required to have a prescription in order to purchase VASCEPA. In addition to distribution agreements with distributors, the Company enters into arrangements with health care providers and payors that provide for government-mandated and/or privately-negotiated rebates, chargebacks and discounts with respect to the purchase of the Company’s product. Revenues from product sales are recognized when the distributor obtains control of the Company’s product, which occurs at a point in time, typically upon delivery to the distributor. Payments from distributors are generally received 30-60 days from the date of sale. The Company evaluates the creditworthiness of each of its distributors to determine whether revenues can be recognized upon delivery, subject to satisfaction of the other requirements, or whether recognition is required to be delayed until receipt of payment . Reserves for Variable Consideration Revenues from product sales are recorded at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established and which result from (a) trade allowances, such as invoice discounts for prompt pay and distributor fees, (b) estimated government and private payor rebates and chargebacks and discounts, such as Medicaid reimbursements, (c) reserves for expected product returns and (d) estimated costs of incentives that are offered within contracts between the Company and its distributors, health care providers, payors and other indirect customers relating to the Company’s sales of its product. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to the distributor) or as a current liability (if the amount is payable to a party other than a distributor). Where appropriate, these estimates take into consideration a range of possible outcomes which are probability-weighted for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the contract. The amount of variable consideration which is included in the transaction price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s estimates, the Company adjusts these estimates, which would affect net product revenue and earnings in the period such variances become known. Trade Allowances: The Company generally provides invoice discounts on VASCEPA sales to its distributors for prompt payment and fees for distribution services, such as fees for certain data that distributors provide to the Company. The payment terms for sales to distributors generally include a 2% discount for prompt payment while the fees for distribution services are based on contractual rates agreed with the respective distributors. Based on historical data, the Company expects its distributors to earn these discounts and fees, and deducts the full amount of these discounts and fees from its gross product revenues and accounts receivable at the time such revenues are recognized. Rebates, Chargebacks and Discounts: The Company contracts with Medicaid, Medicare, other government agencies and various private organizations, or collectively, Third-party Payors, so that VASCEPA will be eligible for purchase by, or partial or full reimbursement from, such Third-party Payors. The Company estimates the rebates, chargebacks and discounts it will provide to Third-party Payors and deducts these estimated amounts from its gross product revenues at the time the revenues are recognized. The Company estimates these reserves based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company estimates the rebates, chargebacks and discounts that it will provide to Third-party Payors based upon (i) the Company’s contracts with these Third-party Payors, (ii) the government-mandated discounts applicable to government-funded programs, (iii) information obtained from the Company’s distributors and (iv) information obtained from other third parties regarding the payor mix for VASCEPA. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. Product Returns: The Company’s distributors have the right to return unopened unprescribed VASCEPA during the 18-month period beginning six months prior to the labeled expiration date and ending twelve months after the labeled expiration date. The expiration date for VASCEPA 1-gram and 0.5-gram size capsules is currently four years and three years, respectively, after being converted into capsule form, which is the last step in the manufacturing process for VASCEPA and generally occurs within a few months before VASCEPA is delivered to distributors. The Company estimates future product returns on sales of VASCEPA based on: (i) data provided to the Company by its distributors (including weekly reporting of distributors’ sales and inventory held by distributors that provided the Company with visibility into the distribution channel in order to determine what quantities were sold to retail pharmacies and other providers), (ii) information provided to the Company from retail pharmacies, (iii) data provided to the Company by a third-party data provider which collects and publishes prescription data, and other third parties, (iv) historical industry information regarding return rates for similar pharmaceutical products, (v) the estimated remaining shelf life of VASCEPA previously shipped and currently being shipped to distributors and (vi) contractual agreements intended to limit the amount of inventory maintained by the Company’s distributors. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. Other Incentives: Other incentives that the Company offers to indirect customers include co-pay mitigation rebates provided by the Company to commercially insured patients who have coverage for VASCEPA and who reside in states that permit co-pay mitigation programs. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for VASCEPA’s purchase price to a specified dollar amount. Based upon the terms of the program and information regarding programs provided for similar specialty pharmaceutical products, the Company estimates the average co-pay mitigation amounts and the percentage of patients that it expects to participate in the program in order to establish its accruals for co-pay mitigation rebates. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. The Company adjusts its accruals for co-pay mitigation rebates based on actual redemption activity and estimates regarding the portion of issued co-pay mitigation rebates that it estimates will be redeemed. The following tables summarize activity in each of the net product revenue allowance and reserve categories described above for the nine months ended September 30, 2020 and 2019: In thousands Trade Allowances Rebates, Chargebacks and Discounts Product Returns Other Incentives Total Balance as of December 31, 2019 $ 29,261 $ 90,997 $ 4,579 $ 3,720 $ 128,557 Provision related to current period sales 95,239 437,030 2,534 50,403 585,206 Provision related to prior period sales — (3,872 ) — — (3,872 ) Credits/payments made for current period sales (32,364 ) (304,903 ) — (46,768 ) (384,035 ) Credits/payments made for prior period sales (29,067 ) (85,731 ) (223 ) (3,721 ) (118,742 ) Balance as of September 30, 2020 $ 63,069 $ 133,521 $ 6,890 $ 3,634 $ 207,114 In thousands Trade Allowances Rebates, Chargebacks and Discounts Product Returns Other Incentives Total Balance as of December 31, 2018 $ 19,495 $ 41,634 $ 2,948 $ 1,167 $ 65,244 Provision related to current period sales 62,177 274,439 1,635 30,882 369,133 Provision related to prior period sales — (204 ) — — (204 ) Credits/payments made for current period sales (34,400 ) (184,801 ) 5 (30,404 ) (249,600 ) Credits/payments made for prior period sales (19,325 ) (41,363 ) (653 ) (1,199 ) (62,540 ) Balance as of September 30, 2019 $ 27,947 $ 89,705 $ 3,935 $ 446 $ 122,033 Such net product revenue allowances and reserves are included within accrued expenses and other current liabilities within the condensed consolidated balance sheets, with the exception of trade allowances and chargebacks, which are included within accounts receivable, net as discussed below. Licensing Revenue The Company enters into licensing agreements which are within the scope of Topic 606 , In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. In determining performance obligations, management evaluates whether the license is distinct from the other performance obligations with the collaborative partner based on the consideration of the relevant facts and circumstances for each arrangement. Factors considered in the determination include the stage of development of the license delivered, research and development capabilities of the partner and the ability of partners to develop and commercialize VASCEPA independent of the Company. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, regulatory and commercial milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone as well as the level of effort and investment required. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development, regulatory and commercial milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect licensing revenues and earnings in the period of adjustment. The Company receives payments from its customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

Development, Commercialization

Development, Commercialization and Supply Agreements	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Development, Commercialization and Supply Agreements	(10) Development, Commercialization and Supply Agreements In-licenses Mochida Pharmaceutical Co., Ltd. In June 2018, the Company entered into a collaboration with Mochida Pharmaceutical Co., Ltd., or Mochida, related to the development and commercialization of drug products and indications based on the active pharmaceutical ingredient in VASCEPA, the omega-3 acid, EPA, or eicosapentaenoic acid. Among other terms in the agreement, the Company obtained an exclusive license to certain Mochida intellectual property to advance the Company’s interests in the United States and certain other territories and the parties will collaborate to research and develop new products and indications based on EPA for the Company’s commercialization in the United States and certain other territories. The potential new product and indication opportunities contemplated under this agreement are currently in early stages of development. Upon closing of the collaboration agreement, the Company made a non-refundable, non-creditable upfront payment of approximately $2.7 million. In addition, the agreement provides for the Company to pay milestone payments upon the achievement of certain product development milestones and royalties on net sales of future products arising from the collaboration, if any. In January 2020, the Company achieved certain milestones under the agreement, resulting in payment of $1.0 million to Mochida, which was recorded as Research and development expense on the condensed consolidated statement of operations. Out-licenses Eddingpharm (Asia) Macao Commercial Offshore Limited In February 2015, the Company entered into a Development, Commercialization and Supply Agreement, or the DCS Agreement, with Eddingpharm (Asia) Macao Commercial Offshore Limited, or Eddingpharm, related to the development and commercialization of VASCEPA in Mainland China, Hong Kong, Macau and Taiwan, or the China Territory. Under the terms of the DCS Agreement, the Company granted to Eddingpharm an exclusive (including as to the Company) license with right to sublicense to develop and commercialize VASCEPA in the China Territory for uses that are currently commercialized and under development by the Company based on the Company’s MARINE, ANCHOR and REDUCE-IT clinical trials of VASCEPA. Under the DCS Agreement, Eddingpharm is solely responsible for development and commercialization activities in the China Territory and associated expenses. The Company provides development assistance and is responsible for supplying finished and later bulk drug product at defined prices under negotiated terms. The Company retains all VASCEPA manufacturing rights. Eddingpharm agreed to certain restrictions regarding the commercialization of competitive products globally and the Company agreed to certain restrictions regarding the commercialization of competitive products in the China Territory. The Company and Eddingpharm agreed to form a joint development committee to oversee regulatory and development activities for VASCEPA in the China Territory in accordance with a negotiated development plan and to form a separate joint commercialization committee to oversee VASCEPA commercialization activities in the China Territory. Development costs are paid by Eddingpharm to the extent such costs are incurred in connection with the negotiated development plan or otherwise incurred by Eddingpharm. Eddingpharm is responsible for preparing and filing regulatory applications in all countries of the China Territory at Eddingpharm’s cost with the Company’s assistance. The DCS Agreement also contains customary provisions regarding indemnification, supply, record keeping, audit rights, reporting obligations, and representations and warranties that are customary for an arrangement of this type. The term of the DCS Agreement expires, on a product-by-product basis, upon the later of (i) the date on which such product is no longer covered by a valid claim under a licensed patent in the China Territory, or (ii) the twelfth (12th) anniversary of the first commercial sale of such product in Mainland China. The DCS Agreement may be terminated by either party in the event of a bankruptcy of the other party and for material breach, subject to customary cure periods. In addition, at any time following the third anniversary of the first commercial sale of a product in Mainland China, Eddingpharm has the right to terminate the DCS Agreement for convenience with twelve months’ prior notice. Neither party may assign or transfer the DCS Agreement without the prior consent of the other party, provided that the Company may assign the DCS Agreement in the event of a change of control transaction. Upon closing of the DCS Agreement, the Company received a non-refundable $15.0 million up-front payment. In March 2016, Eddingpharm submitted its clinical trial application, or CTA, with respect to the MARINE indication for VASCEPA to the Chinese regulatory authority. Following the CTA submission, the Company received a non-refundable $1.0 million milestone payment. In March 2017, the CTA was approved by the Chinese regulatory authority, and, in December 2017, Eddingpharm commenced a pivotal clinical trial aimed to support the regulatory approval of the first indication of VASCEPA in a patient population with severe hypertriglyceridemia in Mainland China. In addition to the non-refundable, up-front and regulatory milestone payments described above, the Company is entitled to receive certain regulatory and sales-based milestone payments of up to an additional $153.0 million as well as tiered double-digit percentage royalties on net sales of VASCEPA in the China Territory escalating to the high teens. The regulatory milestone events relate to the submission and approval of certain applications to the applicable regulatory authority, such as a clinical trial application, clinical trial exemption, or import drug license application. The amounts to be received upon achievement of the regulatory milestone events relate to the submission and approval for three indications, and range from $2.0 million to $15.0 million for a total of $33.0 million. The sales-based milestone events occur when annual aggregate net sales of VASCEPA in the territory equals or exceeds certain specified thresholds, and range from $5.0 million to $50.0 million for a total of $120.0 million. Each such milestone payment shall be payable only once regardless of how many times the sales milestone event is achieved. Each such milestone payment is non-refundable and non-creditable against any other milestone payments. The Company assessed this arrangement in accordance with Topic 606 and concluded that the contract counterparty, Eddingpharm, is a customer. The Company identified the following performance obligations at the inception of the DCS Agreement: (1) the exclusive license to develop and commercialize VASCEPA in the China Territory for uses that are currently commercialized and under development by the Company, (2) the obligation to participate in various steering committees, and (3) ongoing development and regulatory assistance. Based on the analysis performed, the Company concluded that the identified performance obligations are not distinct and therefore a combined performance obligation. The transaction price includes the $15.0 million up-front consideration received and the $1.0 million milestone payment received related to the successful submission of the CTA for the MARINE indication. None of the other clinical or regulatory milestones have been included in the transaction price, as all milestone amounts are fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During the nine months ended September 30, 2020 and 2019, the Company recognized $2.2 million and $0.2 million, respectively, as licensing revenue related to the up-front and milestone payments received in connection with the Eddingpharm agreement. From contract inception through September 30, 2020 and December 31, 2019, the Company recognized $5.2 million and $3.0 million, respectively, as licensing revenue under the DCS Agreement concurrent with the support provided by Amarin to Eddingpharm in achieving the combined development and regulatory performance obligation, which in the Company’s judgment is the best measure of progress towards satisfying this performance obligation. The remaining transaction price of $10.8 million and $13.0 million is recorded in deferred revenue as of September 30, 2020 and December 31, 2019, respectively, on the condensed consolidated balance sheets and will be recognized as revenue over the remaining period of 14 years. Biologix FZCo In March 2016, the Company entered into an agreement with Biologix FZCo, or Biologix, a company incorporated under the laws of the United Arab Emirates, to register and commercialize VASCEPA in several Middle Eastern and North African countries. Under the terms of the distribution agreement, the Company granted to Biologix a non-exclusive license to use its trademarks in connection with the importation, distribution, promotion, marketing and sale of VASCEPA in the Middle East and North Africa territory. Upon closing of the agreement, the Company received a non-refundable up-front payment, which will be recognized as revenue over 10 years commencing upon first marketing approval of VASCEPA in the territory. The Company is entitled to receive all payments based on total product sales and pays Biologix a service fee in exchange for its services, whereby the service fee represents a percentage of gross selling price which is subject to a minimum floor price. In March 2018 and July 2018, the Company received approval for VASCEPA as a prescription medication for use in Lebanon and United Arab Emirates, respectively, as an adjunct to diet to reduce triglyceride levels in adult patients with severe hypertriglyceridemia. VASCEPA was launched in Lebanon in June 2018 and in United Arab Emirates in February 2019. The Company recognized net product revenue of $0.5 million and nil for the three months ended September 30, 2020 and 2019, respectively, and $0.5 million and $0.3 million for the nine months ended September 30, 2020 and 2019 , respectively. HLS Therapeutics, Inc. In September 2017, the Company entered into an agreement with HLS Therapeutics Inc., or HLS, a company incorporated under the laws of Canada, to register, commercialize and distribute VASCEPA in Canada. Under the agreement, HLS is responsible for regulatory and commercialization activities and associated costs. The Company is responsible for providing assistance towards local filings, supplying finished product under negotiated supply terms, maintaining intellectual property, and continuing the development and funding of REDUCE-IT related activities. Upon closing of the agreement, the Company received one-half of a non-refundable $5.0 million up-front payment, and received the remaining half on the six-month The Company assessed this arrangement in accordance with Topic 606 and concluded that the contract counterparty, HLS, is a customer. The Company identified the following performance obligations at the inception of the contract: (1) license to HLS to develop, register, and commercialize VASCEPA in Canada, (2) support general development and regulatory activities, and (3) participate in various steering committees. Based on the analysis performed, the Company concluded that the identified performance obligations in the agreement are not distinct and therefore a combined performance obligation. The transaction price includes the $5.0 million up-front consideration, the $2.5 million milestone related to the achievement of the REDUCE-IT trial primary endpoint, the $2.5 million milestone related to obtaining approval from Health Canada and $3.8 million milestone related to obtaining regulatory exclusivity from the OPML. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. During the nine months ended September 30, 2020 and 2019, the Company recognized $3.5 million and $0.9 million, respectively, as licensing revenue related to up-front and milestone payments received in connection with the HLS agreement. From the contract’s inception through September 30, 2020 and December 31, 2019, the Company has recognized $6.4 million and $2.9 million, respectively, as licensing revenue is recognized under the agreement concurrent with the support provided by Amarin to HLS in achieving this performance obligation, which in the Company’s judgment is the best measure of progress towards satisfying the combined development and regulatory performance obligation. The remaining transaction price of $7.4 million and $7.1 million is recorded in deferred revenue as of September 30, 2020 and December 31, 2019, respectively, on the condensed consolidated balance sheets and will be recognized as revenue over the remaining period of 10 years. The Company recognized net product revenue of $8.5 million and nil for the nine months ended September 30, 2020 and 2019, respectively. The following table presents changes in the balances of the Company’s contract assets and liabilities during the nine months ended September 30, 2020 and 2019: In thousands Balance at Beginning of Period Additions Deductions Balance at End of Period Nine months ended September 30, 2020: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,846 $ 3,750 $ (5,691 ) $ 18,905 Nine months ended September 30, 2019: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,710 $ — $ (1,131 ) $ 19,579 During the nine months ended September 30, 2020 and 2019 date, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods: In thousands Nine Months Ended September 30, Revenue recognized in the period from: 2020 2019 Amounts included in contract liability at the beginning of the period $ 3,951 $ 1,131 Performance obligations satisfied in previous periods $ 1,097 $ —

Leases

Leases	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	(11) Leases The Company leases office space under operating leases. The lease liability is initially measured at the present value of the lease payments to be made over the lease term. Lease payments are comprised of the fixed and variable payments to be made by the Company to the lessor during the lease term minus any incentives or rebates or abatements receivable by the Company from the lessor or the owner. Payments for non-lease components do not form part of lease payments. The lease term includes renewal options only if these options are specified in the lease agreement and if failure to exercise the renewal option imposes a significant economic penalty for the Company. As there are no significant economic penalties, renewal cannot be reasonably assured and the lease terms for the office space do not include any renewal options. The Company has not entered into any leases with related parties. The Company accounts for short-term leases (i.e., lease term of 12 months or less) by making the short-term lease policy election and will not apply the recognition and measurement requirements of ASC 842. The Company has determined that the rate implicit in the lease is not determinable and the Company does not have borrowings with similar terms and collateral. Therefore, the Company considered a variety of factors, including the Company’s credit rating, observable debt yields from comparable companies with a similar credit profile and the volatility in the debt market for securities with similar terms, in determining that 11.5% was reasonable to use as the incremental borrowing rate for purposes of the calculation of lease liabilities and a change of 1% would not result in a material change to the Company’s condensed consolidated financial statements. On April 12, 2019 the Company entered into an Office Centre Sharing Agreement for office space in Dublin, Ireland effective May 1, 2019 was scheduled to terminate on April 30, 2020 and was extended for one additional year through April 30, 2021 and can continue to be extended automatically for successive one year periods. On July 4, 2019, the Company entered into an Office Centre Sharing Agreements effective October 1, 2019 for office space in Dublin, Ireland was scheduled to terminate on September 30, 2020 and was extended for one additional year through April 30, 2021 and can be extended automatically for successive one year periods. On August 1, 2020 the Company entered into an Office Centre Sharing Agreement effective September 14, 2020 for office space in Dublin, Ireland which terminates on April 30, 2021 and can be extended automatically for successive one year periods. These leases have been determined to be short-term leases and the Company is committed to making payments of $0.1 million during the next twelve months. On February 5, 2019, the Company entered into a lease agreement for new office space in Bridgewater, New Jersey, or the Lease. The Lease commenced on August 15, 2019, or the Commencement Date, for an 11-year period, with two five-year The table below depicts a maturity analysis of the Company’s undiscounted payments for its operating lease liabilities and their reconciliation with the carrying amount of lease liability presented in the statement of financial position as of September 30, 2020: Undiscounted lease payments ($000s) Remainder of 2020 $ 239 2021 1,475 2022 1,774 2023 1,808 2024 1,842 2025 and thereafter 10,988 Total undiscounted payments $ 18,126 Discount Adjustments $ (7,561 ) Current operating lease liability $ 1,309 Long-term operating lease liability $ 9,255

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Revenue Recognition	Revenue Recognition In accordance with Accounting Standards Codification, or ASC, Topic 606, Revenue from Contracts with Customers
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents consist of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of purchase of 90 days or less. Restricted cash represents cash and cash equivalents pledged to guarantee repayment of certain expenses which may be incurred for business travel under corporate credit cards held by employees.
Accounts Receivable, net	Accounts Receivable, net Accounts receivable, net, comprised of trade receivables, are generally due within 30 days and are stated at amounts due from customers. The Company recognizes an allowance for losses on accounts receivable in an amount equal to the estimated probable losses net of any recoveries. The allowance is based primarily on assessment of specific identifiable customer accounts considered at risk or uncollectible, as well as an analysis of current receivables aging and expected future write-offs. The expense associated with the allowance for doubtful accounts is recognized as Selling, general, and administrative expense. The Company has not historically experienced any significant credit losses. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations. The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2020 and December 31, 2019: In thousands September 30, 2020 December 31, 2019 Gross trade accounts receivable $ 223,579 $ 149,567 Trade allowances (63,069 ) (29,261 ) Chargebacks (12,273 ) (3,876 ) Allowance for doubtful accounts (945 ) — Accounts receivable, net $ 147,292 $ 116,430
Inventory	Inventory The Company states inventories at the lower of cost or net realizable value. Cost is determined based on actual cost using the average cost method. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. An allowance is established when management determines that certain inventories may not be saleable. If inventory cost exceeds expected net realizable value due to obsolescence, damage or quantities in excess of expected demand, changes in price levels or other causes, the Company will reduce the carrying value of such inventory to net realizable value and recognize the difference as a component of cost of goods sold in the period in which it occurs. The Company capitalizes inventory purchases of saleable product from approved suppliers while inventory purchases from suppliers prior to regulatory approval are included as a component of research and development expense. The Company expenses inventory identified for use as marketing samples when they are packaged. The average cost reflects the actual purchase price of VASCEPA active pharmaceutical ingredient, or API.
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences of differences between the carrying amounts and tax bases of assets and liabilities and operating loss carryforwards and other tax attributes using enacted rates expected to be in effect when those differences reverse. Valuation allowances are provided against deferred tax assets that are not more likely than not to be realized. Deferred tax assets and liabilities are classified as non-current in the condensed consolidated balance sheet. The Company provides reserves for potential payments of tax to various tax authorities and does not recognize tax benefits related to uncertain tax positions and other issues. Tax benefits for uncertain tax positions are based on a determination of whether a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized, assuming that the matter in question will be decided based on its technical merits. The Company’s policy is to record interest and penalties in the income tax provision, as applicable. The Company regularly assesses its ability to realize deferred tax assets. Changes in historical earnings performance, future earnings projections, and changes in tax laws, among other factors, may cause the Company to adjust its valuation allowance on deferred tax assets, which would impact the Company’s income tax expense in the period in which it is determined that these factors have changed. Excess tax benefits and deficiencies that arise upon vesting or exercise of share-based payments are recognized as an income tax benefit and expense, respectively, in the condensed consolidated statement of operations. Excess income tax benefits are classified as cash flows from operating activities and cash paid to taxing authorities arising from the withholding of shares from employees are classified as cash flows from financing activities. The Company’s and its subsidiaries’ income tax returns are periodically examined by various tax authorities, including the Internal Revenue Service, or IRS, and states. The IRS began an examination of the Company’s 2018 U.S. income tax return in the first quarter of 2020. Although the outcome of tax audits is always uncertain and could result in significant cash tax payments, the Company does not believe the outcome of this audit will have a material adverse effect on its consolidated financial position or results of operations.
Loss per Share	Loss per Share Basic net loss per share is determined by dividing net loss by the weighted average shares of common stock outstanding during the period. Diluted net loss per share is determined by dividing net loss by diluted weighted average shares outstanding. Diluted weighted average shares outstanding reflects the dilutive effect, if any, of potentially dilutive common shares, such as common stock options calculated using the treasury stock method and convertible preferred stock using the “if-converted” method. In periods with reported net operating losses, all common stock options are deemed anti-dilutive such that basic net loss per share and diluted net loss per share are equal. The Company’s preferred stock is entitled to receive dividends on an as-if-converted basis in the same form as dividends actually paid on common shares. Accordingly, the preferred stock is considered a participating security and the Company is required to apply the two-class method to consider the impact of the preferred stock on the calculation of basic and diluted earnings per share. The Company is in a net loss position for all periods presented and is therefore not required to present the two-class method, however, in the event the Company is in a net income position, the two-class method must be applied for this period by allocating all earnings during the period to common shares and preferred stock based on their contractual entitlements assuming all earnings are distributed. The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2020 and 2019 are as follows: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Net loss—basic and diluted $ (6,788 ) $ (3,462 ) $ (22,926 ) $ (29,713 ) Weighted average shares outstanding—basic and diluted 389,699 350,994 378,770 336,938 Net loss per share—basic and diluted $ (0.02 ) $ (0.01 ) $ (0.06 ) $ (0.09 ) For the three and nine months ended September 30, 2020 and 2019, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Stock options 17,479 16,259 17,479 16,259 Restricted stock and restricted stock units 7,727 9,359 7,727 9,359 Preferred stock, if converted 2,385 28,932 2,385 28,932 Stock options are anti-dilutive during periods of net earnings when the exercise price of the stock options exceeds the market price of the underlying shares on the last day of the reporting period. Restricted stock and restricted stock units are anti-dilutive during periods of net earnings when underlying performance-based vesting requirements were not achieved as of the last day of the reporting period.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents, short-term and long-term investments, and accounts receivable. The Company maintains substantially all of its cash and cash equivalents, and short-term and long-term investments, in financial institutions believed to be of high-credit quality. A significant portion of the Company’s sales are to wholesalers in the pharmaceutical industry. The Company monitors the creditworthiness of customers to whom it grants credit terms and has not experienced any credit losses. The Company does not require collateral or any other security to support credit sales. Three customers individually accounted for 10% or more of the Company’s gross product sales. Customers A, B, and C accounted for 25%, 37%, and 30%, respectively, of gross product sales for the nine months ended September 30, 2020, and represented 37%, 32%, and 25%, respectively, of the gross accounts receivable balance as of September 30, 2020. Customers A, B, and C accounted for 25%, 36%, and 29%, respectively, of gross product sales for the nine months ended September 30, 2019 and represented 42%, 23%, and 28%, respectively, of the gross accounts receivable balance as of September 30, 2019. The Company has not experienced any significant write-offs of its accounts receivable. All customer accounts are actively managed and no losses in excess of amounts reserved are currently expected; however, the Company is monitoring the potential negative impact of COVID-19 on the Company’s customers’ ability to meet their financial obligations.
Concentration of Suppliers	Concentration of Suppliers The Company has contractual freedom to source the API for VASCEPA and to procure other services supporting its supply chain and has entered into supply agreements with multiple suppliers. The Company’s supply of product for commercial sale and clinical trials is dependent upon relationships with third-party manufacturers and suppliers. The Company cannot provide assurance that its efforts to procure uninterrupted supply of VASCEPA to meet market demand will continue to be successful or that it will be able to renew current supply agreements on favorable terms or at all. Significant alteration to or disruption or termination of the Company’s current supply chain, including as a result of COVID-19, or the Company’s failure to enter into new and similar agreements in a timely fashion, if needed, could have a material adverse effect on its business, condition (financial and other), prospects or results of operations. The Company currently has manufacturing agreements with multiple independent FDA-approved API manufacturers and several independent FDA-approved API encapsulators and packagers for VASCEPA manufacturing. Each of these companies has qualified and validated its manufacturing processes and is capable of manufacturing VASCEPA. There can be no guarantee that these or other suppliers with which the Company may contract in the future to manufacture VASCEPA or VASCEPA API will remain qualified to do so to the Company’s specifications or that these and any future suppliers will have the manufacturing capacity to meet anticipated demand for VASCEPA.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company provides disclosure of financial assets and financial liabilities that are carried at fair value based on the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements may be classified based on the amount of subjectivity associated with the inputs to fair valuation of these assets and liabilities using the following three levels: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (i.e., interest rates, yield curves, etc.) and inputs that are derived principally from or corroborated by observable market data by correlation or other means (market corroborated inputs). Level 3—Unobservable inputs that reflect the Company’s estimates of the assumptions that market participants would use in pricing the asset or liability. The Company develops these inputs based on the best information available, including its own data. The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2020 and December 31, 2019 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 81,714 $ 81,714 $ — $ — U.S. Treasury Shares 59,959 59,959 — — Corporate Bonds 200,704 — 200,704 — Commercial Paper 110,858 — 110,858 — Agency Securities 14,027 — 14,027 — Repo Securities 11,000 — 11,000 — Asset Backed Securities 8,887 — 8,887 — Certificate of Deposit 6,129 — 6,129 — Total $ 493,278 $ 141,673 351,605 $ — December 31, 2019 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 10,078 $ 10,078 $ — $ — The carrying amount of the Company’s cash and cash equivalents approximates fair value because of their short-term nature. The cash and cash equivalents consists of cash, deposits with banks and short-term highly liquid money market instruments with remaining maturities at the date of the purchase of 90 days or less. The Company’s held-to-maturity investments are stated at amortized cost, which approximates fair value. The Company does not intend to sell these investment securities and the contractual maturities are not greater than 24 months. Those with maturities greater than 90 days and less than twelve months are included in short-term investments on its condensed consolidated balance sheet. Those with remaining maturities in excess of twelve months are included in long-term investments on its condensed consolidated balance sheet. Unrealized gains or losses on held-to-maturity securities are not recognized until maturity, except other-than-temporary unrealized losses which are recognized in earnings in the period incurred. The Company evaluates securities with unrealized losses to determine whether such losses are other than temporary. Interest on investments is reported in interest income. The unrealized gain for the nine months ended September 30, 2020 and 2019 was $0.9 million and nil, respectively. The carrying amounts of accounts payable and accrued liabilities approximate fair value because of their short-term nature. The carrying amounts and the estimated fair values of debt from royalty-bearing instrument as of September 30, 2020 and December 31, 2019 are as follows: September 30, 2020 December 31, 2019 In thousands Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Debt from royalty-bearing instrument $ 9,387 $ 9,500 $ 49,702 $ 50,400 The estimated fair value of the debt from royalty-bearing instrument is calculated utilizing the same Level 3 inputs utilized in valuing the related derivative liability (see Derivative Liabilities below). The carrying value of the debt from royalty-bearing instrument is net of the unamortized debt discounts and issuance costs as of both September 30, 2020 and December 31, 2019. The carrying value of the debt from the royalty-bearing instrument as of September 30, 2020 approximates fair value because the instrument will be paid in full in the fourth quarter of 2020.
Derivative Liabilities	Derivative Liabilities Derivative financial liabilities are recorded at fair value, with gains and losses arising for changes in fair value recognized in the condensed consolidated statement of operations at each period end while such instruments are outstanding. If the Company issues shares to discharge the liability, the derivative financial liability is derecognized and common stock and additional paid-in capital are recognized on the issuance of those shares. Long-Term Debt Redemption Feature The Company’s December 2012 royalty-bearing instrument financing arrangement (discussed in Note 5—Debt) is scheduled to be fully repaid in the fourth quarter of 2020. Accounting for this instrument since its inception in 2012 has included reporting of an embedded derivative reflect contains a redemption feature whereby, upon a change of control, the Company would be required to repay $150.0 million, less any previously repaid amount. The Company determined this redemption feature to be an embedded derivative, which is carried at fair value and is classified as Level 3 in the fair value hierarchy due to the use of significant unobservable inputs. The fair value of the embedded derivative was calculated using a probability-weighted model incorporating management estimates of future revenues and for a potential change in control, and by determining the fair value of the debt with and without the change in control provision included. The difference between the two was determined to be the fair value of the embedded derivative. The fair value of this derivative liability is remeasured at each reporting period, with changes in fair value recognized in the condensed consolidated statement of operations. As of September 30, 2020, the fair value of the derivative was determined to be nil, and the debt was valued by comparing debt issues of similar companies with (i) remaining terms of between 1.2 and 6.5 years, (ii) coupon rates of between 6.0% and 11.5% and (iii) market yields of between 5.4% and 16.4%. As of December 31, 2019, the fair value of the derivative was determined to be nil based on underlying assumptions, and the debt was valued by comparing debt issues of similar companies with (i) remaining terms of between 1.9 and 7.3 years, (ii) coupon rates of between 6.0% and 11.5% and (iii) market yields of between 5.2% and 16.8%. As such, the Company recognized no gain or loss on change in fair value of derivative liability for the nine months ended September 30, 2020 and 2019. Certain changes in the assumptions used to value the derivative liability, including the probability of a change in control, could potentially result in a change to the carrying value of such liability. Because the remaining amount due from this royalty-bearing instrument is fixed and will be fully paid in the fourth quarter of 2020, any change in the value of this derivative liability will not have any impact on the Company’s aggregate cash payment obligation from this instrument regardless of any potential change in the carrying value of such liability.
Segment and Geographical Information	Segment and Geographical Information Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated on a regular basis by the chief operating decision-maker, or decision-making group, in deciding how to allocate resources to an individual segment and in assessing performance of the segment. The Company currently operates in one business segment, which is the development and commercialization of VASCEPA. A single management team that reports to the Company’s chief decision-maker, who is the Chief Executive Officer, comprehensively manages the business. Accordingly, the Company does not have separately reportable segments.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, and are early adopted by the Company or adopted as of the specified effective date. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808), Clarifying the Interaction between Topic 808 and Topic 606, which clarified that in collaborative arrangements where the counterparty is a customer for a good or service that is a distinct unit of account is required to be accounted for under ASC 606. The Company adopted this standard effective January 1, 2020, which did not have an impact on the Company’s condensed consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, which requires earlier recognition of credit losses on loans and other financial instruments held by entities, including trade receivables. The new standard requires entities to measure all expected credit losses for financial assets held at each reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. The Company adopted this standard effective January 1, 2020, which did not have a material impact on the Company’s condensed consolidated financial statements. The Company also considered the following recent accounting pronouncement which was not yet adopted as of September 30, 2020: In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes, which simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period, the recognition of deferred tax liabilities for outside basis differences, among other simplifications. The new guidance is effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early adoption of all amendments in the same period is permitted. The Company is currently evaluating the impact that this standard will have on the Company’s condensed consolidated financial statements. The Company believes that the impact of other recently issued but not yet adopted accounting pronouncements will not have a material impact on the Company’s condensed consolidated financial position, results of operations, and cash flows, or do not apply to the Company’s operations.

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Impact of Accounts Receivable Reserves on Gross Trade Accounts Receivable Balances	The following table summarizes the impact of accounts receivable reserves on the gross trade accounts receivable balances as of September 30, 2020 and December 31, 2019: In thousands September 30, 2020 December 31, 2019 Gross trade accounts receivable $ 223,579 $ 149,567 Trade allowances (63,069 ) (29,261 ) Chargebacks (12,273 ) (3,876 ) Allowance for doubtful accounts (945 ) — Accounts receivable, net $ 147,292 $ 116,430
Calculation of Net Loss and Number of Shares Used to Compute Basic and Diluted Net Loss per Share	The calculation of net loss and the number of shares used to compute basic and diluted net loss per share for the three and nine months ended September 30, 2020 and 2019 are as follows: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Net loss—basic and diluted $ (6,788 ) $ (3,462 ) $ (22,926 ) $ (29,713 ) Weighted average shares outstanding—basic and diluted 389,699 350,994 378,770 336,938 Net loss per share—basic and diluted $ (0.02 ) $ (0.01 ) $ (0.06 ) $ (0.09 )
Anti-Dilutive Securities Not Included in the Computation of Net Loss or Earnings per Share	For the three and nine months ended September 30, 2020 and 2019, the following potentially dilutive securities were not included in the computation of net loss per share because the effect would be anti-dilutive or because performance criteria were not yet met for awards contingent upon such measures: Three months ended September 30, Nine months ended September 30, In thousands 2020 2019 2020 2019 Stock options 17,479 16,259 17,479 16,259 Restricted stock and restricted stock units 7,727 9,359 7,727 9,359 Preferred stock, if converted 2,385 28,932 2,385 28,932
Estimated Fair Value of Assets and Liability	The following tables present information about the estimated fair value of the Company’s assets and liabilities as of September 30, 2020 and December 31, 2019 and indicate the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value: September 30, 2020 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 81,714 $ 81,714 $ — $ — U.S. Treasury Shares 59,959 59,959 — — Corporate Bonds 200,704 — 200,704 — Commercial Paper 110,858 — 110,858 — Agency Securities 14,027 — 14,027 — Repo Securities 11,000 — 11,000 — Asset Backed Securities 8,887 — 8,887 — Certificate of Deposit 6,129 — 6,129 — Total $ 493,278 $ 141,673 351,605 $ — December 31, 2019 In thousands Total Level 1 Level 2 Level 3 Asset: Money Market Fund $ 10,078 $ 10,078 $ — $ —
Carrying Amounts and Estimated Fair Values of Debt from Royalty-Bearing Instrument	The carrying amounts of accounts payable and accrued liabilities approximate fair value because of their short-term nature. The carrying amounts and the estimated fair values of debt from royalty-bearing instrument as of September 30, 2020 and December 31, 2019 are as follows: September 30, 2020 December 31, 2019 In thousands Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value Debt from royalty-bearing instrument $ 9,387 $ 9,500 $ 49,702 $ 50,400

Intangible Asset (Tables)

Intangible Asset (Tables)	9 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Carrying Value of Intangible Asset	The carrying value as of September 30, 2020 and December 31, 2019 is as follows: In thousands September 30, 2020 December 31, 2019 Technology rights $ 20,081 $ 20,081 Accumulated amortization (5,904 ) (4,823 ) Intangible asset, net $ 14,177 $ 15,258

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories as of September 30, 2020 and December 31, 2019 consist of the following: In thousands September 30, 2020 December 31, 2019 Raw materials $ 32,956 $ 19,455 Work in process 23,386 12,031 Finished goods 92,189 45,283 Total inventory $ 148,531 $ 76,769

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Summarize Activity of the Net Product Revenue Allowance and Reserve Categories	The following tables summarize activity in each of the net product revenue allowance and reserve categories described above for the nine months ended September 30, 2020 and 2019: In thousands Trade Allowances Rebates, Chargebacks and Discounts Product Returns Other Incentives Total Balance as of December 31, 2019 $ 29,261 $ 90,997 $ 4,579 $ 3,720 $ 128,557 Provision related to current period sales 95,239 437,030 2,534 50,403 585,206 Provision related to prior period sales — (3,872 ) — — (3,872 ) Credits/payments made for current period sales (32,364 ) (304,903 ) — (46,768 ) (384,035 ) Credits/payments made for prior period sales (29,067 ) (85,731 ) (223 ) (3,721 ) (118,742 ) Balance as of September 30, 2020 $ 63,069 $ 133,521 $ 6,890 $ 3,634 $ 207,114 In thousands Trade Allowances Rebates, Chargebacks and Discounts Product Returns Other Incentives Total Balance as of December 31, 2018 $ 19,495 $ 41,634 $ 2,948 $ 1,167 $ 65,244 Provision related to current period sales 62,177 274,439 1,635 30,882 369,133 Provision related to prior period sales — (204 ) — — (204 ) Credits/payments made for current period sales (34,400 ) (184,801 ) 5 (30,404 ) (249,600 ) Credits/payments made for prior period sales (19,325 ) (41,363 ) (653 ) (1,199 ) (62,540 ) Balance as of September 30, 2019 $ 27,947 $ 89,705 $ 3,935 $ 446 $ 122,033

Development, Commercializatio_2

Development, Commercialization and Supply Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Changes in Balances of Contract Assets and Liabilities and Revenues Recognized	The following table presents changes in the balances of the Company’s contract assets and liabilities during the nine months ended September 30, 2020 and 2019: In thousands Balance at Beginning of Period Additions Deductions Balance at End of Period Nine months ended September 30, 2020: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,846 $ 3,750 $ (5,691 ) $ 18,905 Nine months ended September 30, 2019: Contract assets $ — $ — $ — $ — Contract liabilities: Deferred revenue $ 20,710 $ — $ (1,131 ) $ 19,579 During the nine months ended September 30, 2020 and 2019 date, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods: In thousands Nine Months Ended September 30, Revenue recognized in the period from: 2020 2019 Amounts included in contract liability at the beginning of the period $ 3,951 $ 1,131 Performance obligations satisfied in previous periods $ 1,097 $ —

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Maturity Analysis of Undiscounted Payments for Operating Lease Liabilities and Reconciliation with Carrying Amount of Lease Liability	The table below depicts a maturity analysis of the Company’s undiscounted payments for its operating lease liabilities and their reconciliation with the carrying amount of lease liability presented in the statement of financial position as of September 30, 2020: Undiscounted lease payments ($000s) Remainder of 2020 $ 239 2021 1,475 2022 1,774 2023 1,808 2024 1,842 2025 and thereafter 10,988 Total undiscounted payments $ 18,126 Discount Adjustments $ (7,561 ) Current operating lease liability $ 1,309 Long-term operating lease liability $ 9,255

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020USD ($)EmployeeSegment	Dec. 31, 2019USD ($)
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of operating segments | Segment	1
Total assets	$ 960,203,000	$ 882,209,000
Cash and liquid short-term and long-term investments	608,000,000
Total current assets	888,545,000	855,005,000
Cash and cash equivalents	207,207,000	644,588,000
Short-term investments	354,655,000
Long-term investments	46,092,000
Accounts receivable, net	147,292,000	116,430,000
Inventory	148,531,000	76,769,000
Debt from royalty-bearing instrument	9,467,000	$ 50,130,000
Other debt outstanding	$ 0
VASCEPA
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Debt and future repayments percentage of net product revenues	10.00%
Sales Representatives and Managers
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of sales professionals | Employee	440
Sales Representatives
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of sales professionals | Employee	400
Direct Sales Force
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of sales professionals | Employee	900
Direct Sales Force And Sales Representatives
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of sales professionals | Employee	800

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2020USD ($)SegmentCustomer	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2012USD ($)
Significant Accounting Policies [Line Items]
Trade receivables, credit period	30 days
Maturities period	24 months
Unrealized gain on held-to-maturity securities	$ 900,000
Number of operating segments | Segment	1
ASU No. 2018-18
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
ASU No. 2018-13
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
ASU No. 2016-13
Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
Minimum
Significant Accounting Policies [Line Items]
Trade receivables, credit period	30 days
Maximum
Significant Accounting Policies [Line Items]
Trade receivables, credit period	60 days
Embedded Derivative Financial Instruments | BioPharma Debt
Significant Accounting Policies [Line Items]
Maximum repayment of future revenue and receivables				$ 150,000,000
Fair value of embedded derivative liability	$ 0		$ 0
Gain (loss) on change in fair value of derivative liabilities	$ 0	$ 0
Embedded Derivative Financial Instruments | BioPharma Debt | Minimum
Significant Accounting Policies [Line Items]
Derivative liability fair value assumption, coupon rate	6.00%		6.00%
Derivative liability fair value assumptions, market yields	5.40%		5.20%
Embedded Derivative Financial Instruments | BioPharma Debt | Maximum
Significant Accounting Policies [Line Items]
Derivative liability fair value assumption, coupon rate	11.50%		11.50%
Derivative liability fair value assumptions, market yields	16.40%		16.80%
Embedded Derivative Financial Instruments | BioPharma Debt | Measurement Input, Expected Term | Minimum
Significant Accounting Policies [Line Items]
Derivative liability fair value assumptions, term	1 year 2 months 12 days		1 year 10 months 24 days
Embedded Derivative Financial Instruments | BioPharma Debt | Measurement Input, Expected Term | Maximum
Significant Accounting Policies [Line Items]
Derivative liability fair value assumptions, term	6 years 6 months		7 years 3 months 18 days
Short Term Investments
Significant Accounting Policies [Line Items]
Maturities period	12 months
Long Term Investments
Significant Accounting Policies [Line Items]
Maturities period	12 months
Money Market Instruments
Significant Accounting Policies [Line Items]
Maturities period	90 days
Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Number of customers | Customer	3
Customer A | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	25.00%	25.00%
Customer A | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	37.00%	42.00%
Customer B | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	37.00%	36.00%
Customer B | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	32.00%	23.00%
Customer C | Gross Product Sales | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	30.00%	29.00%
Customer C | Accounts Receivable | Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	25.00%	28.00%

Significant Accounting Polici_5

Significant Accounting Policies - Summary of Impact of Accounts Receivable Reserves on Gross Trade Accounts Receivable Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross trade accounts receivable	$ 223,579	$ 149,567
Accounts receivable, net	147,292	116,430
Trade Allowances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	(63,069)	(29,261)
Chargebacks
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	(12,273)	$ (3,876)
Allowance for Doubtful Accounts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowances and reserves	$ (945)

Significant Accounting Polici_6

Significant Accounting Policies - Calculation of Net Loss and Number of Shares Used to Compute Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss—basic and diluted	$ (6,788)	$ (3,462)	$ (22,926)	$ (29,713)
Weighted average shares outstanding—basic and diluted	389,699	350,994	378,770	336,938
Net loss per share—basic and diluted	$ (0.02)	$ (0.01)	$ (0.06)	$ (0.09)

Significant Accounting Polici_7

Significant Accounting Policies - Anti-Dilutive Securities Not Included in the Computation of Net Loss per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	2,385	28,932	2,385	28,932
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	17,479	16,259	17,479	16,259
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities	7,727	9,359	7,727	9,359

Significant Accounting Polici_8

Significant Accounting Policies - Estimated Fair Value of Assets and Liability (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Asset:
Asset, fair value	$ 493,278
Money Market Fund
Asset:
Asset, fair value	81,714	$ 10,078
U.S. Treasury Shares
Asset:
Asset, fair value	59,959
Corporate Bonds
Asset:
Asset, fair value	200,704
Commercial Paper
Asset:
Asset, fair value	110,858
Agency Securities
Asset:
Asset, fair value	14,027
Repo Securities
Asset:
Asset, fair value	11,000
Asset Backed Securities
Asset:
Asset, fair value	8,887
Certificate of Deposit
Asset:
Asset, fair value	6,129
Level 1
Asset:
Asset, fair value	141,673
Level 1 | Money Market Fund
Asset:
Asset, fair value	81,714	$ 10,078
Level 1 | U.S. Treasury Shares
Asset:
Asset, fair value	59,959
Level 2
Asset:
Asset, fair value	351,605
Level 2 | Corporate Bonds
Asset:
Asset, fair value	200,704
Level 2 | Commercial Paper
Asset:
Asset, fair value	110,858
Level 2 | Agency Securities
Asset:
Asset, fair value	14,027
Level 2 | Repo Securities
Asset:
Asset, fair value	11,000
Level 2 | Asset Backed Securities
Asset:
Asset, fair value	8,887
Level 2 | Certificate of Deposit
Asset:
Asset, fair value	$ 6,129

Significant Accounting Polici_9

Significant Accounting Policies - Carrying Amounts and Estimated Fair Values of Debt from Royalty-Bearing Instrument (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt from royalty-bearing instrument, carrying value	$ 9,387	$ 49,702
Debt from Royalty-bearing Instrument
Debt Instrument [Line Items]
Debt from royalty-bearing instrument, estimated fair value	$ 9,500	$ 50,400

Intangible Asset - Additional I

Intangible Asset - Additional Information (Detail) £ in Millions, $ in Millions	Dec. 31, 2019USD ($)	Dec. 31, 2019GBP (£)	Sep. 30, 2020
Finite Lived Intangible Assets [Line Items]
Intangible asset estimated weighted- average remaining useful life			9 years 9 months 18 days
Milestone payment achieved | £		£ 5
Increase in intangible assets | $	$ 8.5

Intangible Asset - Schedule of

Intangible Asset - Schedule of Carrying Value of Intangible Asset (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Technology rights	$ 20,081	$ 20,081
Accumulated amortization	(5,904)	(4,823)
Intangible asset, net	$ 14,177	$ 15,258

Inventory - Schedule of Invento

Inventory - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 32,956	$ 19,455
Work in process	23,386	12,031
Finished goods	92,189	45,283
Total inventory	$ 148,531	$ 76,769

Debt - Long-Term Debt from Roya

Debt - Long-Term Debt from Royalty-Bearing Instrument-December 2012 Financing - Additional Information (Detail) - USD ($)	Dec. 06, 2012	Nov. 30, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Disclosure [Line Items]
Long-term debt from royalty-bearing instrument, carrying amount net of unamortized discount			$ 9,387,000	$ 9,387,000		$ 49,702,000
Interest expense, non-cash				601,000	$ 1,282,000
CPPIB
Debt Disclosure [Line Items]
Maximum repayment of future revenue and receivables			9,600,000	9,600,000
Interest repayment on future revenue and receivables			100,000	100,000
Repayment under agreement			13,400,000	$ 42,800,000
CPPIB | Scenario Forecast
Debt Disclosure [Line Items]
Repayment under agreement		$ 9,600,000
VASCEPA
Debt Disclosure [Line Items]
Debt and future repayments percentage of net product revenues				10.00%
VASCEPA | CPPIB
Debt Disclosure [Line Items]
Debt and future repayments percentage of net product revenues				10.00%
BioPharma Debt
Debt Disclosure [Line Items]
Amount received at the closing of the agreement	$ 100,000,000
Maximum repayment of future revenue and receivables	$ 150,000,000
Royalty-Bearing Debt
Debt Disclosure [Line Items]
Gain (loss) on change in fair value of derivative liabilities				$ 0	0
Long-term debt from royalty-bearing instrument, carrying amount net of unamortized discount			$ 9,400,000	9,400,000		$ 49,700,000
Royalty-Bearing Debt | Cash
Debt Disclosure [Line Items]
Interest expense, contractual coupon interest				1,500,000	3,400,000
Royalty-Bearing Debt | Non Cash
Debt Disclosure [Line Items]
Interest expense, non-cash				$ 600,000	$ 1,300,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Sep. 30, 2020 $ in Millions	USD ($)	GBP (£)
Commitments And Contingencies Disclosure [Line Items]
Potential payable amount over the agreement terms based on minimum purchase obligation	$ 164.7
Further Indication for AMR101 | Marketing Approval In Europe
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment	9.7	£ 7,500,000
Further Indication for AMR101 | Potential Marketing Approval 1
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment	6.4	5,000,000
Further Indication for AMR101 | Potential Marketing Approval 2
Commitments And Contingencies Disclosure [Line Items]
Potential aggregate stock or cash payment	$ 6.4	£ 5,000,000

Equity - Preferred Stock - Addi

Equity - Preferred Stock - Additional Information (Detail)

Sep. 30, 2020£ / sharesshares

Jul. 18, 2019shares

Mar. 05, 2015USD ($)shares

Jul. 30, 2020shares

Apr. 30, 2020shares

Mar. 31, 2020

Sep. 30, 2019USD ($)

Mar. 31, 2015USD ($)

Jun. 30, 2019

Dec. 31, 2019£ / sharesshares

Mar. 05, 2015£ / sharesshares

Mar. 05, 2015$ / sharesshares

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 | $

$ 440,108,000

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

0.1

0.1

Preferred stock, equivalent ordinary shares upon future consolidation outstanding

2,385,078

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

Conversion of stock, shares converted

328,300,010

27,753,000

237,713,680

Series A Preferred Stock | Minimum

Stockholders Equity Note [Line Items]

Beneficial ownership limitation

4.99%

9.90%

Series A Preferred Stock | Maximum

Stockholders Equity Note [Line Items]

Beneficial ownership limitation

19.90%

Ordinary Shares

Stockholders Equity Note [Line Items]

Conversion of Series A Convertible Preferred Stock, net (in shares)

32,830,001

2,775,300

23,771,368

Preferred stock, equivalent ordinary shares upon future consolidation outstanding

2,385,078

American Depositary Shares

Stockholders Equity Note [Line Items]

Issuance of stock (shares)

22,222,223

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

Equity - Common Stock - Additio

Equity - Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions	Mar. 16, 2020£ / sharesshares	Jul. 29, 2019USD ($)	Jul. 18, 2019$ / sharesshares	Sep. 30, 2020£ / sharesshares	Sep. 30, 2019shares	Dec. 31, 2019£ / shares	Mar. 05, 2015£ / shares
Stockholders Equity Note [Line Items]
Common stock, par value | £ / shares				£ 0.50		£ 0.50	£ 0.50
2011 Plan
Stockholders Equity Note [Line Items]
Number of shares remaining under the plan				2,634,440
Amarin Corporation Plc 2017 Employee Stock Purchase Plan | Ordinary Shares
Stockholders Equity Note [Line Items]
Issuance of common stock, net of transaction costs (shares)				123,608	47,358
American Depositary Shares
Stockholders Equity Note [Line Items]
Issuance of common stock, net of transaction costs (shares)			22,222,223
American Depository Shares Ratio			1
Sale of stock price per share | $ / shares			$ 18
American Depositary Shares | Over-Allotment Option
Stockholders Equity Note [Line Items]
Sale of stock price per share | $ / shares			$ 18
Issuance of stock (shares), exercised			3,333,333
Gross proceeds from public offering including exercised option | $		$ 460
Net proceeds from public offering including exercised option | $		$ 440.1
American Depositary Shares | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Expiration date of stock incentive plan	2030-07
American Depositary Shares | Stock Incentive Plan 2020 | Ordinary Shares
Stockholders Equity Note [Line Items]
Common stock, par value | £ / shares	£ 0.50
Issuance of common stock, net of transaction costs (shares)	20,000,000

Equity - Incentive Equity Award

Equity - Incentive Equity Awards - Additional Information (Detail) - USD ($) $ in Thousands	Jul. 13, 2020	Jul. 01, 2020	Mar. 02, 2020	Feb. 03, 2020	May 20, 2019	Feb. 01, 2019	Jun. 01, 2020	Sep. 30, 2020	Sep. 30, 2019
Stockholders Equity Note [Line Items]
Shares issued, exercise of stock options								642,756	5,122,107
Proceeds from exercise of stock options, net of transaction costs								$ 1,861	$ 19,544
Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Stock options, outstanding								17,478,906
Restricted Stock Units (RSUs)
Stockholders Equity Note [Line Items]
Shares issued, related to the vesting of RSUs								1,206,494	1,533,061
Treasury shares for settlement of employee tax obligations								440,573	580,765
Restricted Stock Units (RSUs) | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Restricted stock units, outstanding								7,727,158
Percentage of outstanding shares on a fully diluted basis								2.00%
Stock units, Granted			821,950		45,163	757,800
Stock units, Vesting Period			3 years		3 years	3 years	3 years
Stock units, additional granted					20,000
Restricted Stock Units (RSUs) | Stock Incentive Plan 2011 | Employees
Stockholders Equity Note [Line Items]
Stock units, Granted		100,000		1,253,400		580,000	782,520
Restricted Stock Units (RSUs) | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Stock units, Granted	164,657
Stock units, Vesting Period	3 years
Stock Options | Stock Incentive Plan 2011
Stockholders Equity Note [Line Items]
Percentage of outstanding shares on a fully diluted basis								4.00%
Stock units, Vesting Period				4 years		4 years
Stock options, Granted				1,875,000	58,721	1,193,400
Stock Options | Stock Incentive Plan 2020
Stockholders Equity Note [Line Items]
Stock options, Granted	210,764
Performance-Based RSUs
Stockholders Equity Note [Line Items]
Shares issued, related to the vesting of RSUs								1,107,660
Treasury shares for settlement of employee tax obligations								461,820

Co-Promotion Agreement - Additi

Co-Promotion Agreement - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2018	Dec. 31, 2019
Co Promotion Agreement [Line Items]
Accrued expenses and other current liabilities	$ 189,650		$ 139,826
Co-Promotion Agreement | Kowa Pharmaceuticals America, Inc.
Co Promotion Agreement [Line Items]
Agreement amended year	2017
Promotion fee as a percentage of gross margin		18.50%
Maximum co-promotion tail payments receive period	3 years
Co-promotion tail payments receivable		$ 17,800
Accrued co- promotion tail payments		$ 16,600
Accrued expenses and other liabilities	$ 5,200		10,000
Accrued expenses and other current liabilities	$ 3,900		$ 6,500

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	30 days
Sales discount percentage	2.00%
Effect of significant financing component when transfer and customer payment of good or service occurs within one year or less	true
VASCEPA 1-Gram
Disaggregation Of Revenue [Line Items]
Product expiration date after being converted into capsule form	4 years
VASCEPA 0.5-Gram
Disaggregation Of Revenue [Line Items]
Product expiration date after being converted into capsule form	3 years
Minimum
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	30 days
Maximum
Disaggregation Of Revenue [Line Items]
Payment period from distributors received from date of sale	60 days

Revenue Recognition - Summarize

Revenue Recognition - Summarize Activity of the Net Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 128,557	$ 65,244
Provision related to current period sales	585,206	369,133
Provision related to prior period sales	(3,872)	(204)
Credits/payments made for current period sales	(384,035)	(249,600)
Credits/payments made for prior period sales	(118,742)	(62,540)
Ending balance	207,114	122,033
Trade Allowances
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	29,261	19,495
Provision related to current period sales	95,239	62,177
Credits/payments made for current period sales	(32,364)	(34,400)
Credits/payments made for prior period sales	(29,067)	(19,325)
Ending balance	63,069	27,947
Rebates, Chargebacks and Discounts
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	90,997	41,634
Provision related to current period sales	437,030	274,439
Provision related to prior period sales	(3,872)	(204)
Credits/payments made for current period sales	(304,903)	(184,801)
Credits/payments made for prior period sales	(85,731)	(41,363)
Ending balance	133,521	89,705
Product Returns
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	4,579	2,948
Provision related to current period sales	2,534	1,635
Credits/payments made for current period sales		5
Credits/payments made for prior period sales	(223)	(653)
Ending balance	6,890	3,935
Other Incentives
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance	3,720	1,167
Provision related to current period sales	50,403	30,882
Credits/payments made for current period sales	(46,768)	(30,404)
Credits/payments made for prior period sales	(3,721)	(1,199)
Ending balance	$ 3,634	$ 446

Development, Commercializatio_3

Development, Commercialization and Supply Agreement - Additional Information (Detail)	1 Months Ended						3 Months Ended		9 Months Ended		12 Months Ended	28 Months Ended	37 Months Ended	59 Months Ended	68 Months Ended
	Feb. 29, 2020USD ($)	Jan. 31, 2020USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Mar. 31, 2016USD ($)	Feb. 28, 2015USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)Item	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2020USD ($)
License And Collaboration Agreements [Line Items]
Revenue recognized related to upfront and milestone payments									$ 5,691,000	$ 1,131,000
Licenses revenue							$ 156,499,000	$ 112,408,000	446,809,000	286,478,000
Deferred revenue							18,905,000	19,579,000	18,905,000	19,579,000	$ 20,710,000	$ 20,846,000	$ 18,905,000	$ 20,846,000	$ 18,905,000
Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue							155,190,000	$ 112,250,000	$ 441,118,000	285,347,000
Mochida | In-licenses
License And Collaboration Agreements [Line Items]
Milestones payment		$ 1,000,000
Mochida | In-licenses | Research and Development Expense
License And Collaboration Agreements [Line Items]
Upfront payment											$ 2,700,000
Eddingpharm | Out-licenses
License And Collaboration Agreements [Line Items]
Non-refundable up-front received						$ 15,000,000
Number of indications of the regulatory milestone events relating to the submission and approval | Item									3
Amounts to be received upon achievement of the regulatory milestone events									$ 33,000,000
Sales-based milestone event payment									120,000,000
Revenue recognized related to upfront and milestone payments									2,200,000	200,000
Deferred revenue							10,800,000		10,800,000			13,000,000	10,800,000	13,000,000	10,800,000
Eddingpharm | Out-licenses | Licensing Revenue
License And Collaboration Agreements [Line Items]
Licenses revenue														3,000,000	5,200,000
Eddingpharm | Out-licenses | Maximum
License And Collaboration Agreements [Line Items]
Additional upfront payment eligible to receive based on development, regulatory and sales Milestone									153,000,000
Amounts to be received upon achievement of the regulatory milestone events									15,000,000
Sales-based milestone event payment									50,000,000
Eddingpharm | Out-licenses | Minimum
License And Collaboration Agreements [Line Items]
Amounts to be received upon achievement of the regulatory milestone events									2,000,000
Sales-based milestone event payment									5,000,000
Eddingpharm | Out-licenses | Clinical Trial Application
License And Collaboration Agreements [Line Items]
Non-refundable milestone payment					$ 1,000,000
Biologix FZCo | Out-licenses
License And Collaboration Agreements [Line Items]
Revenue recognition period of non-refundable up-front payment					10 years
Biologix FZCo | Out-licenses | Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue							500,000		500,000	300,000
HLS | Out-licenses
License And Collaboration Agreements [Line Items]
Non-refundable up-front received				$ 5,000,000
Non-refundable milestone payment	$ 2,500,000	$ 3,800,000	$ 2,500,000	$ 2,500,000
Revenue recognized related to upfront and milestone payments									3,500,000	900,000
Deferred revenue							$ 7,400,000		7,400,000			7,100,000	7,400,000	$ 7,100,000	$ 7,400,000
Non-refundable up-front received period				6 months
Non-refundable milestone payment received				$ 3,800,000
HLS | Out-licenses | Licensing Revenue
License And Collaboration Agreements [Line Items]
Licenses revenue												$ 2,900,000	$ 6,400,000
HLS | Out-licenses | Product Revenue, Net
License And Collaboration Agreements [Line Items]
Licenses revenue									$ 8,500,000	$ 0
HLS | Out-licenses | Maximum
License And Collaboration Agreements [Line Items]
Additional upfront payment eligible to receive based on development, regulatory and sales Milestone				$ 50,000,000

Development, Commercializatio_4

Development, Commercialization and Supply Agreement - Additional Information (Detail 1) - Out-licenses - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-10-01	Sep. 30, 2020
HLS
License And Collaboration Agreements [Line Items]
Revenue recognized over remaining period	10 years
Eddingpharm
License And Collaboration Agreements [Line Items]
Revenue recognized over remaining period	14 years

Development, Commercializatio_5

Development, Commercialization and Supply Agreement - Changes in Balances of Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 20,846	$ 20,710
Deferred revenue, Additions	3,750
Deferred revenue, Deductions	(5,691)	(1,131)
Deferred revenue, Balance at End of Period	$ 18,905	$ 19,579

Development, Commercializatio_6

Development, Commercialization and Supply Agreement - Recognized Revenues Changes in Contract Asset and Contract Liability Balances (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Revenue recognized in the period from:
Amounts included in contract liability at the beginning of the period	$ 3,951	$ 1,131
Performance obligations satisfied in previous periods	$ 1,097

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	Aug. 01, 2020	Aug. 15, 2019USD ($)RenewalOption	Jul. 04, 2019	Apr. 12, 2019	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Lessee Lease Description [Line Items]
Incremental borrowing rate for purposes of calculation of lease liabilities					11.50%		11.50%
Change in incremental borrowing rate							1.00%
Short-term lease payments					$ 1,475		$ 1,475
Monthly rent payment					18,126		18,126
Operating lease liability					10,600		10,600		$ 9,800
Operating lease right-of-use asset					8,149		8,149		$ 8,511
Operating lease expense					$ 400	$ 400	$ 1,200	$ 1,100
Dublin | Office Centre Sharing Agreements
Lessee Lease Description [Line Items]
Description of lease agreement							On April 12, 2019 the Company entered into an Office Centre Sharing Agreement for office space in Dublin, Ireland effective May 1, 2019 was scheduled to terminate on April 30, 2020 and was extended for one additional year through April 30, 2021 and can continue to be extended automatically for successive one year periods. On July 4, 2019, the Company entered into an Office Centre Sharing Agreements effective October 1, 2019 for office space in Dublin, Ireland was scheduled to terminate on September 30, 2020 and was extended for one additional year through April 30, 2021 and can be extended automatically for successive one year periods. On August 1, 2020 the Company entered into an Office Centre Sharing Agreement effective September 14, 2020 for office space in Dublin, Ireland which terminates on April 30, 2021 and can be extended automatically for successive one year periods.
Operating lease, expiration date	Apr. 30, 2021		Sep. 30, 2020	Apr. 30, 2020
Lease renewal term					1 year		1 year
Operating lease, option to additional extend							extended for one additional year through April 30, 2021 and can continue to be extended automatically for successive one year periods
Lease termination existence of option to extend							true
Operating lease, existence of option to extend [true false]							true
Operating lease, option to extend							On July 4, 2019, the Company entered into an Office Centre Sharing Agreements effective October 1, 2019 for office space in Dublin, Ireland was scheduled to terminate on September 30, 2020 and was extended for one additional year through April 30, 2021 and can be extended automatically for successive one year periods. On August 1, 2020 the Company entered into an Office Centre Sharing Agreement effective September 14, 2020 for office space in Dublin, Ireland which terminates on April 30, 2021 and can be extended automatically for successive one year periods.
Short-term lease payments					$ 100		$ 100
Dublin | Office Centre Sharing Agreements Effective May 1, 2019
Lessee Lease Description [Line Items]
Operating lease, expiration date				Apr. 30, 2021
Bridgewater
Lessee Lease Description [Line Items]
Description of lease agreement							Amarin will have a one-time option to terminate the agreement effective on the first day of the ninety-seventh month after the Commencement Date upon advance written notice and a termination payment specified in the Lease.
Lease renewal term		5 years
Lease termination existence of option to extend		true
Lease commencement date		Aug. 15, 2019
Lease agreement term		11 years
Number of renewal options | RenewalOption		2
Lease termination description							one-time option to terminate the agreement effective on the first day of the ninety-seventh month after the Commencement Date
Monthly rent payment		$ 100
Maximum
Lessee Lease Description [Line Items]
Short term lease period							12 months

Leases - Maturity Analysis of U

Leases - Maturity Analysis of Undiscounted Payments for Operating Lease Liabilities and Reconciliation with Carrying Amount of Lease Liability (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Undiscounted lease payments
Remainder of 2020	$ 239
2021	1,475
2022	1,774
2023	1,808
2024	1,842
2025 and thereafter	10,988
Total undiscounted payments	18,126
Discount Adjustments	(7,561)
Current operating lease liability	1,309
Long-term operating lease liability	$ 9,255	$ 9,443