<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>242</ContextCount>
  <ElementCount>374</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>91</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CondensedConsolidatedStatementsOfOperations</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CondensedConsolidatedStatementsOfComprehensiveLoss</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/ConsolidatedStatementsOfStockholdersEquity</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1005000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Description of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DescriptionOfBusiness</Role>
      <ShortName>Description of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Basis of Presentation and Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Discontinued Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DiscontinuedOperations</Role>
      <ShortName>Discontinued Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Revenue Recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognition</Role>
      <ShortName>Revenue Recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/MarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Property and Equipment, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/PropertyAndEquipmentNet</Role>
      <ShortName>Property and Equipment, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Goodwill and Intangible Assets, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNet</Role>
      <ShortName>Goodwill and Intangible Assets, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Current Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CurrentLiabilities</Role>
      <ShortName>Current Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Accumulated Other Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - Equity-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EquityBasedCompensation</Role>
      <ShortName>Equity-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2117100 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Acquisitions, Collaboration, License and Other Strategic Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreements</Role>
      <ShortName>Acquisitions, Collaboration, License and Other Strategic Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2121100 - Disclosure - Restructuring Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RestructuringExpenses</Role>
      <ShortName>Restructuring Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2122100 - Disclosure - Recently Issued and Proposed Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RecentlyIssuedAndProposedAccountingPronouncements</Role>
      <ShortName>Recently Issued and Proposed Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Recently Adopted Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RecentlyAdoptedAccountingPronouncements</Role>
      <ShortName>Recently Adopted Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Basis of Presentation and Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2302302 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Basis of Presentation and Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Discontinued Operations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DiscontinuedOperationsTables</Role>
      <ShortName>Discontinued Operations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/DiscontinuedOperations</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Revenue Recognition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionTables</Role>
      <ShortName>Revenue Recognition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/RevenueRecognition</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/MarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/MarketableSecurities</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/FairValueMeasurements</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/Inventories</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2308301 - Disclosure - Property and Equipment, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/PropertyAndEquipmentNetTables</Role>
      <ShortName>Property and Equipment, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/PropertyAndEquipmentNet</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Goodwill and Intangible Assets, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNetTables</Role>
      <ShortName>Goodwill and Intangible Assets, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNet</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Current Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CurrentLiabilitiesTables</Role>
      <ShortName>Current Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/CurrentLiabilities</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/IncomeTaxes</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Accumulated Other Comprehensive Loss (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AccumulatedOtherComprehensiveLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/AccumulatedOtherComprehensiveLoss</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2315301 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/EarningsPerShare</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - Equity-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EquityBasedCompensationTables</Role>
      <ShortName>Equity-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/EquityBasedCompensation</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/CommitmentsAndContingencies</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - Acquisitions, Collaboration, License and Other Strategic Agreements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreementsTables</Role>
      <ShortName>Acquisitions, Collaboration, License and Other Strategic Agreements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreements</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2320301 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/Debt</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2321301 - Disclosure - Restructuring Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RestructuringExpensesTables</Role>
      <ShortName>Restructuring Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/RestructuringExpenses</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2402403 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies - Restricted Cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesRestrictedCashDetails</Role>
      <ShortName>Basis of Presentation and Summary of Significant Accounting Policies - Restricted Cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2402404 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies - Concentration and Significant Customer Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesConcentrationAndSignificantCustomerInformationDetails</Role>
      <ShortName>Basis of Presentation and Summary of Significant Accounting Policies - Concentration and Significant Customer Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Discontinued Operations - Summary of Net Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DiscontinuedOperationsSummaryOfNetIncomeDetails</Role>
      <ShortName>Discontinued Operations - Summary of Net Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2403403 - Disclosure - Discontinued Operations - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DiscontinuedOperationsNarrativeDetails</Role>
      <ShortName>Discontinued Operations - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Revenue Recognition - Disaggregated Revenue By Products (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionDisaggregatedRevenueByProductsDetails</Role>
      <ShortName>Revenue Recognition - Disaggregated Revenue By Products (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - Revenue Recognition - Total Gross Product  (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionTotalGrossProductDetails</Role>
      <ShortName>Revenue Recognition - Total Gross Product  (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2404404 - Disclosure - Revenue Recognition - Product Revenue Allowance and Accrual Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionProductRevenueAllowanceAndAccrualActivityDetails</Role>
      <ShortName>Revenue Recognition - Product Revenue Allowance and Accrual Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2404405 - Disclosure - Revenue Recognition - Remaining Performance Obligation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionRemainingPerformanceObligationDetails</Role>
      <ShortName>Revenue Recognition - Remaining Performance Obligation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2404406 - Disclosure - Revenue Recognition - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RevenueRecognitionNarrativeDetails</Role>
      <ShortName>Revenue Recognition - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/MarketableSecuritiesDetails</Role>
      <ShortName>Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/MarketableSecuritiesTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/FairValueMeasurementsAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2406403 - Disclosure - Fair Value Measurements - Contingent Consideration (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/FairValueMeasurementsContingentConsiderationDetails</Role>
      <ShortName>Fair Value Measurements - Contingent Consideration (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2406404 - Disclosure - Fair Value Measurements - Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/FairValueMeasurementsDebtDetails</Role>
      <ShortName>Fair Value Measurements - Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/InventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/InventoriesTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2408402 - Disclosure - Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/PropertyAndEquipmentNetDetails</Role>
      <ShortName>Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/PropertyAndEquipmentNetTables</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Goodwill and Intangible Assets, Net - Schedule of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNetScheduleOfIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Intangible Assets, Net - Schedule of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Goodwill and Intangible Assets, Net - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNetNarrativeDetails</Role>
      <ShortName>Goodwill and Intangible Assets, Net - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2409404 - Disclosure - Goodwill and Intangible Assets, Net - Schedule of Expected Future Annual Amortization Expense related to Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/GoodwillAndIntangibleAssetsNetScheduleOfExpectedFutureAnnualAmortizationExpenseRelatedToIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Intangible Assets, Net - Schedule of Expected Future Annual Amortization Expense related to Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Current Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CurrentLiabilitiesDetails</Role>
      <ShortName>Current Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/CurrentLiabilitiesTables</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Income Taxes - Schedule of Effective Income Tax Rate and Income Tax Expense (Benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/IncomeTaxesScheduleOfEffectiveIncomeTaxRateAndIncomeTaxExpenseBenefitDetails</Role>
      <ShortName>Income Taxes - Schedule of Effective Income Tax Rate and Income Tax Expense (Benefit) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Income Taxes - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/IncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Accumulated Other Comprehensive Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AccumulatedOtherComprehensiveLossDetails</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/AccumulatedOtherComprehensiveLossTables</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2415402 - Disclosure - Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/EarningsPerShareTables</ParentRole>
      <Position>69</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - Equity-Based Compensation - Activity Related to Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EquityBasedCompensationActivityRelatedToPlansDetails</Role>
      <ShortName>Equity-Based Compensation - Activity Related to Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2416403 - Disclosure - Equity-Based Compensation - Equity-Based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/EquityBasedCompensationEquityBasedCompensationExpenseDetails</Role>
      <ShortName>Equity-Based Compensation - Equity-Based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2417401 - Disclosure - Stockholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/StockholdersEquityDetails</Role>
      <ShortName>Stockholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/StockholdersEquity</ParentRole>
      <Position>72</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CommitmentsAndContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/CommitmentsAndContingenciesTables</ParentRole>
      <Position>73</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2418403 - Disclosure - Commitments and Contingencies - Operating Leases Maturity, After Adoption of Topic 842 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CommitmentsAndContingenciesOperatingLeasesMaturityAfterAdoptionOfTopic842Details</Role>
      <ShortName>Commitments and Contingencies - Operating Leases Maturity, After Adoption of Topic 842 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2418404 - Disclosure - Commitments and Contingencies - Operating Leases Maturity, Before Adoption of Topic 842 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/CommitmentsAndContingenciesOperatingLeasesMaturityBeforeAdoptionOfTopic842Details</Role>
      <ShortName>Commitments and Contingencies - Operating Leases Maturity, Before Adoption of Topic 842 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - Acquisitions, Collaboration, License and Other Strategic Agreements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreementsDetails</Role>
      <ShortName>Acquisitions, Collaboration, License and Other Strategic Agreements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreementsTables</ParentRole>
      <Position>76</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2419403 - Disclosure - Acquisitions, Collaboration, License and Other Strategic Agreements - Assets Acquired and Liabilities Assumed Related to the Business Combination (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/AcquisitionsCollaborationLicenseAndOtherStrategicAgreementsAssetsAcquiredAndLiabilitiesAssumedRelatedToBusinessCombinationDetails</Role>
      <ShortName>Acquisitions, Collaboration, License and Other Strategic Agreements - Assets Acquired and Liabilities Assumed Related to the Business Combination (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2420402 - Disclosure - Debt - Schedule of Outstanding Debt Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DebtScheduleOfOutstandingDebtObligationsDetails</Role>
      <ShortName>Debt - Schedule of Outstanding Debt Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2420403 - Disclosure - Debt - Outstanding Convertible Note Balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DebtOutstandingConvertibleNoteBalancesDetails</Role>
      <ShortName>Debt - Outstanding Convertible Note Balances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2420404 - Disclosure - Debt - Convertible Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.amagpharma.com/role/DebtConvertibleNotesDetails</Role>
      <ShortName>Debt - Convertible Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2420405 - Disclosure - Debt - Total Interest Expense Recognized Related to the Convertible Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.amagpharma.com/role/DebtTotalInterestExpenseRecognizedRelatedToConvertibleNotesDetails</Role>
      <ShortName>Debt - Total Interest Expense Recognized Related to the Convertible Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2420406 - Disclosure - Debt - Future Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/DebtFuturePaymentsDetails</Role>
      <ShortName>Debt - Future Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2421402 - Disclosure - Restructuring Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RestructuringExpensesDetails</Role>
      <ShortName>Restructuring Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.amagpharma.com/role/RestructuringExpensesTables</ParentRole>
      <Position>83</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>2423401 - Disclosure - Recently Adopted Accounting Pronouncements - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.amagpharma.com/role/RecentlyAdoptedAccountingPronouncementsNarrativeDetails</Role>
      <ShortName>Recently Adopted Accounting Pronouncements - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="amag-20190331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items - amag-20190331.xml</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/role/uncategorizedFacts</Role>
      <ShortName>Uncategorized Items - amag-20190331.xml</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>amag-20190331.xml</File>
    <File>amag-20190331.xsd</File>
    <File>amag-20190331_cal.xml</File>
    <File>amag-20190331_def.xml</File>
    <File>amag-20190331_lab.xml</File>
    <File>amag-20190331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
