| Cover | Oct. 08, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 8, 2019 |
| Entity File Number | 001-10865 |
| Entity Registrant Name | AMAG PHARMACEUTICALS, INC. |
| Entity Central Index Key | 0000792977 |
| Entity Tax Identification Number | 04-2742593 |
| Entity Incorporation, State or Country Code | DE |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | AMAG |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
