Summarizes Activity of the Net Product Revenue Allowance and Reserve Categories (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 7,090	$ 2,469
Provision related to current period and deferred sales	9,745	4,299
Provision related to prior period sales	74amrn_ProvisionRelatedToPriorPeriodSales	12amrn_ProvisionRelatedToPriorPeriodSales
Credits/payments made for current period and deferred sales	(2,835)	(2,148)
Credits/payments made for prior period sales	(5,529)	(1,837)
Ending balance	8,545	2,795
Allowance for Trade Receivables
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	2,207	1,071
Provision related to current period and deferred sales	2,756	1,400
Credits/payments made for current period and deferred sales	(462)	(411)
Credits/payments made for prior period sales	(1,555)	(926)
Ending balance	2,946	1,134
Rebates Chargebacks And Discounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	3,610	1,137
Provision related to current period and deferred sales	5,145	1,930
Provision related to prior period sales	74
Credits/payments made for current period and deferred sales	(1,288)	(765)
Credits/payments made for prior period sales	(3,367)	(911)
Ending balance	4,174	1,391
Allowance for Sales Returns
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	481	72
Provision related to current period and deferred sales	127	68
Provision related to prior period sales		12
Ending balance	608	152
Other Incentive Programs
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	792	189
Provision related to current period and deferred sales	1,717	901
Credits/payments made for current period and deferred sales	(1,085)	(972)
Credits/payments made for prior period sales	(607)
Ending balance	$ 817	$ 118

Credits/payments Made for Prior Period Sales

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- Definition

Provision Related to Prior Period Sales

+ References

No definition available.

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- 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

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 09

-Article 12

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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.

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