Cover Page - shares	3 Months Ended
	Mar. 31, 2020	May 06, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-10865
Entity Registrant Name	AMAG Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2742593
Entity Address, Address Line One	1100 Winter Street,
Entity Address, City or Town	Waltham,
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	617
Local Phone Number	498-3300
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	AMAG
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		34,272,805
Entity Central Index Key	0000792977
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false