Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 02, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
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 sharePreferred Share Purchase Rights
Trading Symbol	AMAG
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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 Public Float			$ 335.0
Entity Common Stock, Shares Outstanding (in shares)		34,265,738
Entity Central Index Key	0000792977
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	true
Amendment Description	AMAG Pharmaceuticals, Inc (the “Company” or “we”) is filing this Amendment No. 1 on Form 10-K/A (this “Amendment”) to amend and restate certain items in its Annual Report on Form 10-K for the year ended December 31, 2019, originally filed with the U.S. Securities and Exchange Commission (the “SEC”) on March 6, 2020 (the “Original 10-K”). The Company identified immaterial errors in its previously reported revenue over the impacted annual periods of 2016 through 2019 and, in connection therewith, the Company’s management identified a material weakness in our internal control over financial reporting (“ICFR”) related to ensuring the timely recognition of our gross-to-net adjustments for certain governmental rebates and the related accruals. Accordingly, this Amendment is being filed to amend Item 6, Selected Financial Data, Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations, Item 8, Financial Statements and Supplementary Data, and Item 9A, Controls and Procedures, of Part II of the Original 10-K and restate the financial statements and related notes to reflect the immaterial errors identified, Management’s Annual Report on Internal Control Over Financial Reporting, management’s assessment of the effectiveness of our disclosure controls and procedures and PwC’s Report of Independent Registered Public Accounting Firm on the Company’s internal control over financial reporting.