Business Combinations - Activity - Lumara (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		3 Months Ended	6 Months Ended
	Nov. 12, 2014	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Business Combinations
Common stock, par value (in dollars per share)			$ 0.01		$ 0.01
Fair values assigned to assets acquired and the liabilities assumed
Goodwill			$ 639,484		$ 639,188
Other disclosures
Net deferred tax liability			188,852		$ 189,145
Acquisition-related costs		$ 2,653		$ 2,653
Lumara Health
Business Combinations
Ownership percentage acquired	100.00%
Additional merger consideration based upon achievement of certain net sales milestones
Future contingent payments, maximum	$ 350,000
Components of total purchase price:
Cash consideration	600,000
Fair value of AMAG common stock issued	111,964
Fair value of contingent milestone payments	205,000
Estimated working capital and other adjustments	821
Purchase price paid at closing	917,785
Less: Cash received on finalization of the net working capital and other adjustments	(562)
Cash acquired from Lumara Health	(5,219)
Total purchase price	912,004
Fair values assigned to assets acquired and the liabilities assumed
Accounts receivable	36,852
Inventories	30,300
Prepaid and other current assets	3,322
Deferred income tax assets	102,355
Property and equipment	60
Restricted cash - short-term	1,997
Other long-term assets	3,412
Accounts payable	(3,807)
Accrued expenses	(36,561)
Deferred income tax liabilities	(295,676)
Other long-term liabilities	(4,563)
Total estimated identifiable net assets	713,891
Goodwill	198,113		$ 198,100
Total	912,004
Other disclosures
Discount rate (as a percent)			5.00%
Lumara Health | Makena IPR&D
Fair values assigned to assets acquired and the liabilities assumed
Indefinite-lived intangible assets	79,100
Lumara Health | Makena base technology
Fair values assigned to assets acquired and the liabilities assumed
Finite-lived intangible assets	797,100
Indemnification Escrow Fund | Lumara Health
Other disclosures
Escrow fund	$ 35,000
Common Stock | Lumara Health
Business Combinations
Shares of AMAG common stock issued in business combination	3.2