Accounts receivable credit period

No definition available.

Name:	amrn_AccountsReceivableCreditPeriod
Namespace Prefix:	amrn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Derivative liability fair value assumptions expected term.

+ References

No definition available.

+ Details

Name:	amrn_DerivativeLiabilityFairValueAssumptionsExpectedTerm
Namespace Prefix:	amrn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value assumptions, comparable yield to maturity.

+ References

No definition available.

+ Details

Name:	amrn_FairValueAssumptionsComparableYieldToMaturity
Namespace Prefix:	amrn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value assumptions coupon rate.

+ References

No definition available.

+ Details

Name:	amrn_FairValueAssumptionsCouponRate
Namespace Prefix:	amrn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Held to maturity securities continuous unrealized gain position fair value.

+ References

No definition available.

+ Details

Name:	amrn_HeldToMaturitySecuritiesContinuousUnrealizedGainPositionFairValue
Namespace Prefix:	amrn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of customers.

+ References

No definition available.

+ Details

Name:	amrn_NumberOfCustomers
Namespace Prefix:	amrn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Significant accounting policies.

+ References

No definition available.

+ Details

Name:	amrn_SignificantAccountingPoliciesLineItems
Namespace Prefix:	amrn_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13537-108611

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624163-113959

+ Details

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

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8672-108599

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EmbeddedDerivativeFinancialInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=amrn_BiopharmaceuticalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputExpectedTermMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=amrn_LongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=amrn_MoneyMarketInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=amrn_CustomerAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=amrn_CustomerBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=amrn_CustomerCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant Accounting Policies - Additional Information (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) Segment Customer	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2012 USD ($)
Significant Accounting Policies [Line Items]
Trade receivables, credit period	30 days
Maturities period	24 months
Unrealized gain on held-to-maturity securities	$ 1,300
Number of operating segments \| Segment	1
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				$ 150,000,000.0
Fair value of embedded derivative liability		$ 0	$ 0
Gain (loss) on change in fair value of derivative liabilities		$ 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		6.10%	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		17.60%	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 4 months 24 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 9 months 18 days	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%	24.00%
Customer A \| Accounts Receivable \| Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	32.00%	38.00%
Customer B \| Gross Product Sales \| Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	37.00%	37.00%
Customer B \| Accounts Receivable \| Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	38.00%	32.00%
Customer C \| Gross Product Sales \| Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	29.00%	29.00%
Customer C \| Accounts Receivable \| Customer Concentration Risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	23.00%	22.00%