Additional cash received from collaborators to reimburse certain expenses

No definition available.

Name:	amag_AdditionalUpfrontPaymentReceived
Namespace Prefix:	amag_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the milestone payments received under the agreement.

+ References

No definition available.

+ Details

Name:	amag_CollaborativeArrangementMilestonePaymentsReceived
Namespace Prefix:	amag_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Initial term (in years) of the exclusive license to develop and commercialize Feraheme under the collaboration agreement.

+ References

No definition available.

+ Details

Name:	amag_CollaborativeArrangementsLicenseTerm
Namespace Prefix:	amag_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the maximum percentage of royalty receivable by the entity under the collaboration agreement.

+ References

No definition available.

+ Details

Name:	amag_CollaborativeArrangementsMaximumPercentageOfRoyaltiesReceivable
Namespace Prefix:	amag_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the potential milestone payments expected to be received by the entity under the collaboration agreement.

+ References

No definition available.

+ Details

Name:	amag_CollaborativeArrangementsPotentialMilestonePaymentsExpectedToBeReceived
Namespace Prefix:	amag_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of deliverables under the License, Development and Commercialization Agreement, or the Takeda Agreement.

+ References

No definition available.

+ Details

Name:	amag_NumberOfDeliverables
Namespace Prefix:	amag_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of years over which the amount of previously reported deferred or unearned revenue is recognized as revenue.

+ References

No definition available.

+ Details

Name:	amag_RecognitionOfDeferredRevenueAmortizationPeriod
Namespace Prefix:	amag_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

Amount of previously reported deferred or unearned revenue that was recognized as revenue during the period. Deferred revenue is a liability related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 13.A.4(a).Q1)

-URI http://asc.fasb.org/extlink&oid=6600647&loc=d3e214044-122780

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

+ Details

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

- Definition

Cash received from collaborators during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 27

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

+ Details

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

- Definition

Repayment received or receivable for expenses incurred on behalf of a client or customer, other than those reimbursements received by landlords from tenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 45

-Section 45

-Paragraph 23

-URI http://asc.fasb.org/extlink&oid=21915142&loc=d3e60722-111653

+ Details

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

- Definition

The amount of consideration recognized during the period for the milestone or milestones.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 28

-Section 50

-Paragraph 2

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=19771982&loc=SL6892177-166501

+ Details

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

Collaborative Agreements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2012	Jun. 30, 2012	Apr. 30, 2010 Takeda	Mar. 31, 2010 Takeda	Dec. 31, 2012 Takeda item	Dec. 31, 2012 Takeda item	Dec. 31, 2011 Takeda	Dec. 31, 2010 Takeda	Dec. 31, 2008 3SBio License Agreement	Dec. 31, 2012 3SBio License Agreement Canada
Collaborative Agreements
Upfront payment received			$ 60.0						$ 1.0
Additional upfront payment								1.0
Milestone payments expected to be received under the agreement					186.0	186.0
Milestone revenue received					18.0	33.0
Milestone payments revenue recognized under the agreement	5.0	15.0
Number of deliverables					4	4
Other reimbursement revenues						0.4	2.0	1.6
Period of recognition of deferred revenues				10 years
Deferred revenue recognized in earnings related to upfront payment						$ 6.1	$ 6.1	$ 4.6
Initial term of license									13 years
Maximum percentage of royalties receivable										25.00%