Summarize Activity of the Net Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 27,198	$ 15,796
Provision related to current period sales	30,426	18,309
Provision related to prior period sales	(1,082)	(709)
Credits/payments made for current period sales	(4,416)	(3,013)
Credits/payments made for prior period sales	(20,262)	(10,518)
Ending balance	31,864	19,865
Trade Allowances
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	3,743	4,296
Provision related to current period sales	6,621	4,218
Provision related to prior period sales	(298)	(274)
Credits/payments made for current period sales	(2,357)	(1,463)
Credits/payments made for prior period sales	(3,107)	(2,734)
Ending balance	4,602	4,043
Rebates, Chargebacks and Discounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	20,915	9,881
Provision related to current period sales	19,670	11,455
Provision related to prior period sales	(702)	(435)
Credits/payments made for current period sales	(727)	(1,228)
Credits/payments made for prior period sales	(15,376)	(6,418)
Ending balance	23,780	13,255
Product Returns
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	859	535
Provision related to current period sales	1,028	107
Credits/payments made for prior period sales	(9)	(82)
Ending balance	1,878	560
Other Incentives
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	1,681	1,084
Provision related to current period sales	3,107	2,529
Provision related to prior period sales	(82)
Credits/payments made for current period sales	(1,332)	(322)
Credits/payments made for prior period sales	(1,770)	(1,284)
Ending balance	$ 1,604	$ 2,007

Credits/payments made for prior period sales.

No definition available.

Name:	amrn_CreditsPaymentsMadeForPriorPeriodSales
Namespace Prefix:	amrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Provision related to prior period sales.

+ References

No definition available.

+ Details

Name:	amrn_ProvisionRelatedToPriorPeriodSales
Namespace Prefix:	amrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

+ Details

Name:	us-gaap_ValuationAllowancesAndReservesBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to costs and expenses.

+ References

+ Details

Name:	us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively.

+ References

+ Details

Name:	us-gaap_ValuationAllowancesAndReservesDeductions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=us-gaap_AllowanceForTradeReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=amrn_RebatesChargebacksAndDiscountsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=us-gaap_AllowanceForSalesReturnsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=amrn_OtherIncentiveProgramsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: