Description of Business (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2012 Takeda	Dec. 31, 2012 Takeda
Description of Business
Milestone payments received under the agreement		$ 18.0	$ 33.0
Revenue from product sales and royalties			0.1
Payment made to licensees	$ 1.6

Represents the amount of revenue earned from product sales and royalties on sales of products earned by the entity pursuant to the collaboration agreement.

No definition available.

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