Debt	12 Months Ended
Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	(7) 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 December 31, 2018, the remaining amount to be repaid to CPPIB is $88.6 million. During the year ended December 31, 2018, the Company made repayments under the agreement of $20.5 million to CPPIB and an additional $7.7 million was paid in February 2019 for the fourth quarter of 2018. These payments, as well as additional quarterly repayments scheduled in the future, are calculated as 10% of Vascepa net revenues. All such payments reduce 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. The Company can prepay the net remaining amount at any time. 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 difference between the two fair values of the debt was determined to be the fair value of the embedded derivative, and upon closing the Company recorded a derivative liability of $14.6 million as a reduction to the note payable. The fair value of this derivative liability is remeasured at each reporting period, with changes in fair value recognized in the 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 years ended December 31, 2018 and 2017. As of December 31, 2018 and 2017, the carrying value of the royalty-bearing instrument, net of the unamortized debt discount and issuance costs, was $79.7 million and $92.4 million, respectively. During the year ended December 31, 2018, the Company recorded cash and non-cash interest expense of $5.6 million and $2.0 million, respectively, in connection with the royalty-bearing instrument. During the year ended December 31, 2017, the Company recorded $6.4 million and $2.1 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. January 2012, May 2014, and November 2015 Exchangeable Senior Notes In 2012, 2014 and 2015, the Company and its subsidiaries entered into a series of transactions pertaining to exchangeable notes. In January 2017, holders of the 3.5% exchangeable senior notes due 2032 (the “2012 Notes”) exercised their option to put approximately $15.0 million in aggregate principal amount of 2012 Notes to the Company for cash and, in March 2017, the Company redeemed the entirety of the remaining $0.1 million in aggregate principal amount of 2012 Notes. The carrying value of the related conversion option will remain in equity hereafter as a result of the repayment in full of the related debt instrument. As of December 31, 2018 and 2017, all debt issued in these transactions was exchanged or redeemed such that none remained outstanding. January 2017 Exchangeable Senior Notes On January 20, 2017, the Company and Corsicanto II DAC (“Corsicanto II”), a designated activity company formed under the laws of Ireland and a wholly owned subsidiary of the Company, entered into separate, privately negotiated purchase agreements with certain investors pursuant to which Corsicanto II issued and sold $30.0 million in aggregate principal amount of 3.5% exchangeable senior notes due 2047 (the “2017 Notes”) at an issue price of 100%. The net proceeds from the offering were $28.8 million after deducting placement agent fees and offering expenses payable by the Company. The 2017 Notes were issued pursuant to an Indenture (the “Indenture”) entered into by the Company, Corsicanto II and Wilmington Trust, National Association, as trustee (the “Trustee”). The 2017 Notes were the senior unsecured obligations of Corsicanto II and were guaranteed by the Company. The offering of the 2017 Notes closed on January 25, 2017. In October 2018, Corsicanto II mandatorily exchanged $30.0 million of aggregate principal amount of the 2017 Notes for equity upon satisfaction of specified equity conditions as described below, such that no 2017 Notes remained outstanding as of December 31, 2018. Corsicanto II has no assets, operations, revenues or cash flows other than those related to the issuance, administration and repayment of the 2017 Notes. The 2017 Notes Indenture contained a provision that allowed the Company to elect, at its option, to cause all or any portion of the 2017 Notes to be mandatorily exchanged in whole or in part at any time prior to the close of business on the business day preceding January 15, 2047 if the Daily VWAP (as defined in the Indenture) equaled or exceeded 130% of the Exchange Price then in effect (which quotient equals approximately $5.05 on the date thereof) for at least 20 VWAP Trading Days (as defined in the Indenture) in any 30 VWAP Trading Day period, and upon satisfaction of other specified equity conditions, including that the ADSs issuable upon exchange of the 2017 Notes be eligible for resale without registration by non-affiliates and listed on The NASDAQ Global Market, its related exchanges or the New York Stock Exchange. In October 2018, Corsicanto II gave notice to the holders of the 2017 Notes that the above described conditions had been satisfied and exercised its option to mandatorily exchange $30.0 million of aggregate principal amount of the 2017 Notes for equity with settlement in November 2018, such that all of the outstanding 2017 Notes were retired. The initial exchange rate was 257.2016 ADSs per $1,000 principal amount of the 2017 Notes (equivalent to an initial exchange price of approximately $3.89 per ADS (the “Exchange Price”)), subject to adjustment in certain circumstances, including, but not limited to, the payment of cash dividends. The initial exchange price for the 2017 Notes represented a premium of approximately 35% over the last reported sale price of $2.88 per share of the Company’s ADSs on The NASDAQ Global Market on January 19, 2017. Upon exchange, the 2017 Notes were settled in ADSs. Consistent with the 2017 Notes Indenture, no adjustment was needed such that the final exchange rate was 257.2016 ADSs per $1,000 of principal amount, resulting in the issuance of 7,716,046 ADSs in exchange for the 2017 Notes. Upon exchange, the Company settled $30.0 million of aggregate principal amount of the 2017 Notes ($29.2 million in carrying value, net of unamortized issuance costs) and recognized $5.0 million in common stock and $24.4 million in additional paid-in capital. Included within this $24.4 million is $0.3 million of accrued but unpaid interest as of the exchange date deemed satisfied and discharged in full upon delivery of the ADSs consistent with the terms of the notes and ASC 470-20, less $0.1 million of transaction costs. The 2017 Notes had a stated interest of 3.5% per annum from, and including, January 25, 2017, payable semi-annually in arrears on January 15 and July 15 of each year, beginning on July 15, 2017 and ending upon the 2017 Notes’ maturity date of January 15, 2047, had the notes not been exchanged early. The 2017 Notes Indenture provided holders the option to exchange the 2017 Notes for ADSs at any time after the issuance of the 2017 Notes and prior to the close of business on the second business day immediately preceding January 15, 2047 at the initial exchange rate. If a Fundamental Change (as defined in the 2017 Notes Indenture) had occurred prior to the 2017 Notes being exchanged, holders could have required the Company to repurchase all or part of their 2017 Notes for cash at a Fundamental Change repurchase price equal to 100% of the aggregate principal amount of the 2017 Notes to be repurchased, plus accrued and unpaid interest to, but not including, the Fundamental Change repurchase date. Corsicanto II agreed to use commercially reasonable efforts to procure the listing of the 2017 Notes on the Global Exchange Market operated under the supervision of the Irish Stock Exchange (or on another recognized stock exchange for the purposes of Section 64 of the Taxes Consolidation Act 1997 of Ireland and within the meaning of Section 1005 ITA 2007 of the United Kingdom) prior to July 15, 2017, which was the first interest payment date for the 2017 Notes. The 2017 Notes were recorded at par of $30.0 million. In addition, the Company recorded a discount of $1.2 million in placement agent fees and offering expenses. Such costs were presented as a direct deduction from the debt liability on the consolidated balance sheet as of December 31, 2017. This discount was amortized as interest expense over the estimated life of the 2017 Notes, through the first optional put date in January 2022. As of December 31, 2018 and 2017, the carrying value of the 2017 Notes, net of unamortized discount, was nil and $29.0 million, respectively. Because the conversion option in the 2017 Notes received an exception from derivative accounting and only required gross physical settlement in shares, the embedded option did not require separate accounting and was therefore accounted for as part of the debt host at amortized cost. In addition, the Company determined that the fundamental change redemption feature was clearly and closely related to the debt host in accordance with ASC 815-15 and therefore did not require bifurcation. During the year ended December 31, 2018, the Company recognized interest expense of $1.1 million related to the 2017 Notes, of which $0.2 million represents non-cash interest and $0.9 million represents contractual coupon interest. During the year ended December 31, 2017, the Company recognized interest expense of $1.2 million related to the 2017 Notes, of which $0.2 million represented non-cash interest and $1.0 million represents contractual coupon interest. As of December 31, 2018 and 2017, the Company had accrued interest of nil and $0.5 million, respectively, related to the 2017 Notes, which is presented as current portion of exchangeable senior notes, net of discount, on the consolidated balance sheets. The Company made the contractual interest payments due on the 2017 Notes during the years ended December 31, 2018 and 2017 of $1.1 million and $0.5 million, respectively.

Debt

12 Months Ended

Dec. 31, 2018

(7) 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 December 31, 2018, the remaining amount to be repaid to CPPIB is $88.6 million. During the year ended December 31, 2018, the Company made repayments under the agreement of $20.5 million to CPPIB and an additional $7.7 million was paid in February 2019 for the fourth quarter of 2018. These payments, as well as additional quarterly repayments scheduled in the future, are calculated as 10% of Vascepa net revenues. All such payments reduce 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. The Company can prepay the net remaining amount at any time.

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 difference between the two fair values of the debt was determined to be the fair value of the embedded derivative, and upon closing the Company recorded a derivative liability of $14.6 million as a reduction to the note payable. The fair value of this derivative liability is remeasured at each reporting period, with changes in fair value recognized in the 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 years ended December 31, 2018 and 2017.

As of December 31, 2018 and 2017, the carrying value of the royalty-bearing instrument, net of the unamortized debt discount and issuance costs, was $79.7 million and $92.4 million, respectively. During the year ended December 31, 2018, the Company recorded cash and non-cash interest expense of $5.6 million and $2.0 million, respectively, in connection with the royalty-bearing instrument. During the year ended December 31, 2017, the Company recorded $6.4 million and $2.1 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.

January 2012, May 2014, and November 2015 Exchangeable Senior Notes

In 2012, 2014 and 2015, the Company and its subsidiaries entered into a series of transactions pertaining to exchangeable notes. In January 2017, holders of the 3.5% exchangeable senior notes due 2032 (the “2012 Notes”) exercised their option to put approximately $15.0 million in aggregate principal amount of 2012 Notes to the Company for cash and, in March 2017, the Company redeemed the entirety of the remaining $0.1 million in aggregate principal amount of 2012 Notes. The carrying value of the related conversion option will remain in equity hereafter as a result of the repayment in full of the related debt instrument. As of December 31, 2018 and 2017, all debt issued in these transactions was exchanged or redeemed such that none remained outstanding.

January 2017 Exchangeable Senior Notes

On January 20, 2017, the Company and Corsicanto II DAC (“Corsicanto II”), a designated activity company formed under the laws of Ireland and a wholly owned subsidiary of the Company, entered into separate, privately negotiated purchase agreements with certain investors pursuant to which Corsicanto II issued and sold $30.0 million in aggregate principal amount of 3.5% exchangeable senior notes due 2047 (the “2017 Notes”) at an issue price of 100%. The net proceeds from the offering were $28.8 million after deducting placement agent fees and offering expenses payable by the Company. The 2017 Notes were issued pursuant to an Indenture (the “Indenture”) entered into by the Company, Corsicanto II and Wilmington Trust, National Association, as trustee (the “Trustee”). The 2017 Notes were the senior unsecured obligations of Corsicanto II and were guaranteed by the Company. The offering of the 2017 Notes closed on January 25, 2017. In October 2018, Corsicanto II mandatorily exchanged $30.0 million of aggregate principal amount of the 2017 Notes for equity upon satisfaction of specified equity conditions as described below, such that no 2017 Notes remained outstanding as of December 31, 2018. Corsicanto II has no assets, operations, revenues or cash flows other than those related to the issuance, administration and repayment of the 2017 Notes.

The 2017 Notes Indenture contained a provision that allowed the Company to elect, at its option, to cause all or any portion of the 2017 Notes to be mandatorily exchanged in whole or in part at any time prior to the close of business on the business day preceding January 15, 2047 if the Daily VWAP (as defined in the Indenture) equaled or exceeded 130% of the Exchange Price then in effect (which quotient equals approximately $5.05 on the date thereof) for at least 20 VWAP Trading Days (as defined in the Indenture) in any 30 VWAP Trading Day period, and upon satisfaction of other specified equity conditions, including that the ADSs issuable upon exchange of the 2017 Notes be eligible for resale without registration by non-affiliates and listed on The NASDAQ Global Market, its related exchanges or the New York Stock Exchange. In October 2018, Corsicanto II gave notice to the holders of the 2017 Notes that the above described conditions had been satisfied and exercised its option to mandatorily exchange $30.0 million of aggregate principal amount of the 2017 Notes for equity with settlement in November 2018, such that all of the outstanding 2017 Notes were retired. The initial exchange rate was 257.2016 ADSs per $1,000 principal amount of the 2017 Notes (equivalent to an initial exchange price of approximately $3.89 per ADS (the “Exchange Price”)), subject to adjustment in certain circumstances, including, but not limited to, the payment of cash dividends. The initial exchange price for the 2017 Notes represented a premium of approximately 35% over the last reported sale price of $2.88 per share of the Company’s ADSs on The NASDAQ Global Market on January 19, 2017. Upon exchange, the 2017 Notes were settled in ADSs. Consistent with the 2017 Notes Indenture, no adjustment was needed such that the final exchange rate was 257.2016 ADSs per $1,000 of principal amount, resulting in the issuance of 7,716,046 ADSs in exchange for the 2017 Notes.

Upon exchange, the Company settled $30.0 million of aggregate principal amount of the 2017 Notes ($29.2 million in carrying value, net of unamortized issuance costs) and recognized $5.0 million in common stock and $24.4 million in additional paid-in capital. Included within this $24.4 million is $0.3 million of accrued but unpaid interest as of the exchange date deemed satisfied and discharged in full upon delivery of the ADSs consistent with the terms of the notes and ASC 470-20, less $0.1 million of transaction costs.

The 2017 Notes had a stated interest of 3.5% per annum from, and including, January 25, 2017, payable semi-annually in arrears on January 15 and July 15 of each year, beginning on July 15, 2017 and ending upon the 2017 Notes’ maturity date of January 15, 2047, had the notes not been exchanged early. The 2017 Notes Indenture provided holders the option to exchange the 2017 Notes for ADSs at any time after the issuance of the 2017 Notes and prior to the close of business on the second business day immediately preceding January 15, 2047 at the initial exchange rate. If a Fundamental Change (as defined in the 2017 Notes Indenture) had occurred prior to the 2017 Notes being exchanged, holders could have required the Company to repurchase all or part of their 2017 Notes for cash at a Fundamental Change repurchase price equal to 100% of the aggregate principal amount of the 2017 Notes to be repurchased, plus accrued and unpaid interest to, but not including, the Fundamental Change repurchase date.

Corsicanto II agreed to use commercially reasonable efforts to procure the listing of the 2017 Notes on the Global Exchange Market operated under the supervision of the Irish Stock Exchange (or on another recognized stock exchange for the purposes of Section 64 of the Taxes Consolidation Act 1997 of Ireland and within the meaning of Section 1005 ITA 2007 of the United Kingdom) prior to July 15, 2017, which was the first interest payment date for the 2017 Notes.

The 2017 Notes were recorded at par of $30.0 million. In addition, the Company recorded a discount of $1.2 million in placement agent fees and offering expenses. Such costs were presented as a direct deduction from the debt liability on the consolidated balance sheet as of December 31, 2017. This discount was amortized as interest expense over the estimated life of the 2017 Notes, through the first optional put date in January 2022. As of December 31, 2018 and 2017, the carrying value of the 2017 Notes, net of unamortized discount, was nil and $29.0 million, respectively.

Because the conversion option in the 2017 Notes received an exception from derivative accounting and only required gross physical settlement in shares, the embedded option did not require separate accounting and was therefore accounted for as part of the debt host at amortized cost. In addition, the Company determined that the fundamental change redemption feature was clearly and closely related to the debt host in accordance with ASC 815-15 and therefore did not require bifurcation.

During the year ended December 31, 2018, the Company recognized interest expense of $1.1 million related to the 2017 Notes, of which $0.2 million represents non-cash interest and $0.9 million represents contractual coupon interest. During the year ended December 31, 2017, the Company recognized interest expense of $1.2 million related to the 2017 Notes, of which $0.2 million represented non-cash interest and $1.0 million represents contractual coupon interest. As of December 31, 2018 and 2017, the Company had accrued interest of nil and $0.5 million, respectively, related to the 2017 Notes, which is presented as current portion of exchangeable senior notes, net of discount, on the consolidated balance sheets. The Company made the contractual interest payments due on the 2017 Notes during the years ended December 31, 2018 and 2017 of $1.1 million and $0.5 million, respectively.