Additional cash received from collaborators to reimburse certain expenses.

No definition available.

Name:	amag_AdditionalUpfrontPaymentReceived
Namespace Prefix:	amag_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Represents the product sales and royalty revenue recognized under the agreement.

+ References

No definition available.

+ Details

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

- 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

Sum of the carrying amounts of deferred costs that are expected to be recognized as a charge against earnings in periods after one year or beyond the normal operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_DeferredCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets 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 SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

Reference 2: 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 Response)

-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

+ Details

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

- 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=27012821&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

Name:	us-gaap_DeferredRevenueRevenueRecognized
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 Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

Name:	us-gaap_ProceedsFromCollaborators
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=26872669&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

Name:	us-gaap_ReimbursementRevenue
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

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

Collaborative Agreements (Details) (Takeda, USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2010	Mar. 31, 2010	Sep. 30, 2013 item	Jun. 30, 2012	Sep. 30, 2013 item	Dec. 31, 2012	Dec. 31, 2010
Collaborative Agreements
Number of deliverables			4		4
Upfront payment received	$ 60.0
Additional upfront payment							1.0
Period of recognition of deferred revenues		10 years
Milestone revenue received						18.0
Deferred revenue recognized in earnings related to upfront payment of an $18.0 million milestone payment			2.0		5.9
Milestone payments revenue recognized under the agreement				15.0
Product sales and royalty revenue recognized			0.1		0.3
Deferred revenues			2.1		2.1
Deferred costs			1.9		1.9
Maximum
Collaborative Agreements
Milestone payments expected to be received under the agreement			186.0		186.0
Other reimbursement revenues			$ 0.1		$ 0.1