<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.3.a.u2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>266</ContextCount>
  <ElementCount>399</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>91</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>10</UnitCount>
  <MyReports>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveLoss</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedStatementsOfStockholdersEquity</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1003501 - Statement - Consolidated Statements of Stockholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedStatementsOfStockholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004000 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Nature of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/NatureOfBusiness</Role>
      <ShortName>Nature of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Property and Equipment, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/PropertyAndEquipmentNet</Role>
      <ShortName>Property and Equipment, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Restricted Cash</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RestrictedCash</Role>
      <ShortName>Restricted Cash</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Cash, Cash Equivalents and Short-term and Long-term Investments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/CashCashEquivalentsAndShortTermAndLongTermInvestments</Role>
      <ShortName>Cash, Cash Equivalents and Short-term and Long-term Investments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Accrued Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/AccruedExpenses</Role>
      <ShortName>Accrued Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Warrants</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/Warrants</Role>
      <ShortName>Warrants</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Significant Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SignificantAgreements</Role>
      <ShortName>Significant Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - 401(k) Savings Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/A401KSavingsPlan</Role>
      <ShortName>401(k) Savings Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - Quarterly Financial Data (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/QuarterlyFinancialDataUnaudited</Role>
      <ShortName>Quarterly Financial Data (unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2302302 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Property and Equipment, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/PropertyAndEquipmentNetTables</Role>
      <ShortName>Property and Equipment, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/PropertyAndEquipmentNet</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Restricted Cash (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RestrictedCashTables</Role>
      <ShortName>Restricted Cash (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/RestrictedCash</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Cash, Cash Equivalents and Short-term and Long-term Investments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/CashCashEquivalentsAndShortTermAndLongTermInvestmentsTables</Role>
      <ShortName>Cash, Cash Equivalents and Short-term and Long-term Investments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/CashCashEquivalentsAndShortTermAndLongTermInvestments</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Accrued Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/AccruedExpensesTables</Role>
      <ShortName>Accrued Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/AccruedExpenses</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Warrants (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/WarrantsTables</Role>
      <ShortName>Warrants (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/Warrants</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/StockholdersEquity</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/StockBasedCompensation</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/IncomeTaxes</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/Leases</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - Quarterly Financial Data (unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/QuarterlyFinancialDataUnauditedTables</Role>
      <ShortName>Quarterly Financial Data (unaudited) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/QuarterlyFinancialDataUnaudited</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2402403 - Disclosure - Summary of Significant Accounting Policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesTables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2402404 - Disclosure - Summary of Significant Accounting Policies - Schedule of Financial Instruments Carried at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesScheduleOfFinancialInstrumentsCarriedAtFairValueDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Financial Instruments Carried at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2402405 - Disclosure - Summary of Significant Accounting Policies - Summary of Changes in the Fair Value of Preferred and Common Stock Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesSummaryOfChangesInFairValueOfPreferredAndCommonStockWarrantsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Summary of Changes in the Fair Value of Preferred and Common Stock Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2402406 - Disclosure - Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLivesOfPropertyAndEquipmentDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2402407 - Disclosure - Summary of Significant Accounting Policies - Schedule of Anti-dilutive Common Stock Equivalents Excluded from the Calculation of Diluted Net Income (Loss) per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SummaryOfSignificantAccountingPoliciesScheduleOfAntiDilutiveCommonStockEquivalentsExcludedFromCalculationOfDilutedNetIncomeLossPerShareDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Anti-dilutive Common Stock Equivalents Excluded from the Calculation of Diluted Net Income (Loss) per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Property and Equipment, Net - Schedule of Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/PropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails</Role>
      <ShortName>Property and Equipment, Net - Schedule of Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Restricted Cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RestrictedCashDetails</Role>
      <ShortName>Restricted Cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/RestrictedCashTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - Restricted Cash - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RestrictedCashNarrativeDetails</Role>
      <ShortName>Restricted Cash - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Cash, Cash Equivalents and Short-term and Long-term Investments - Schedule of Available-for-Sale Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/CashCashEquivalentsAndShortTermAndLongTermInvestmentsScheduleOfAvailableForSaleSecuritiesDetails</Role>
      <ShortName>Cash, Cash Equivalents and Short-term and Long-term Investments - Schedule of Available-for-Sale Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Accrued Expenses - Schedule of Accrued Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/AccruedExpensesScheduleOfAccruedExpensesDetails</Role>
      <ShortName>Accrued Expenses - Schedule of Accrued Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Warrants - Summary of Shares Issuable Upon Exercise of Outstanding Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/WarrantsSummaryOfSharesIssuableUponExerciseOfOutstandingWarrantsDetails</Role>
      <ShortName>Warrants - Summary of Shares Issuable Upon Exercise of Outstanding Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Stockholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockholdersEquityDetails</Role>
      <ShortName>Stockholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/StockholdersEquityTables</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockholdersEquityScheduleOfCommonStockReservedForFutureIssuanceDetails</Role>
      <ShortName>Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2410401 - Disclosure - Significant Agreements - Sotatercept Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SignificantAgreementsSotaterceptAgreementDetails</Role>
      <ShortName>Significant Agreements - Sotatercept Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2410402 - Disclosure - Significant Agreements - REBLOZYL Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SignificantAgreementsReblozylAgreementDetails</Role>
      <ShortName>Significant Agreements - REBLOZYL Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2410403 - Disclosure - Significant Agreements - Accounting Analysis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SignificantAgreementsAccountingAnalysisDetails</Role>
      <ShortName>Significant Agreements - Accounting Analysis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - Significant Agreements - Other (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/SignificantAgreementsOtherDetails</Role>
      <ShortName>Significant Agreements - Other (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Stock-Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationDetails</Role>
      <ShortName>Stock-Based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/StockBasedCompensationTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2411403 - Disclosure - Stock-Based Compensation - Schedule of Total Compensation Cost Recognized for All Stock-based Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationScheduleOfTotalCompensationCostRecognizedForAllStockBasedAwardsDetails</Role>
      <ShortName>Stock-Based Compensation - Schedule of Total Compensation Cost Recognized for All Stock-based Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2411404 - Disclosure - Stock-Based Compensation - Schedule of Stock Option Valuation Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationScheduleOfStockOptionValuationAssumptionsDetails</Role>
      <ShortName>Stock-Based Compensation - Schedule of Stock Option Valuation Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2411405 - Disclosure - Stock-Based Compensation - Summary of Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationSummaryOfStockOptionActivityDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Stock Option Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2411406 - Disclosure - Stock-based Compensation - Schedule of Restricted Stock Unit Activity and Performance-Based Restricted Stock Units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/StockBasedCompensationScheduleOfRestrictedStockUnitActivityAndPerformanceBasedRestrictedStockUnitsDetails</Role>
      <ShortName>Stock-based Compensation - Schedule of Restricted Stock Unit Activity and Performance-Based Restricted Stock Units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2412401 - Disclosure - 401(k) Savings Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/A401KSavingsPlanDetails</Role>
      <ShortName>401(k) Savings Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/A401KSavingsPlan</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/IncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/IncomeTaxesTables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Income Taxes Income Taxes - Components of the Company's Deferred Tax Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/IncomeTaxesIncomeTaxesComponentsOfCompanysDeferredTaxAssetsDetails</Role>
      <ShortName>Income Taxes Income Taxes - Components of the Company's Deferred Tax Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2413404 - Disclosure - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/IncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Leases - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/LeasesNarrativeDetails</Role>
      <ShortName>Leases - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2414403 - Disclosure - Leases - Minimum Lease Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/LeasesMinimumLeasePaymentsDetails</Role>
      <ShortName>Leases - Minimum Lease Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2414404 - Disclosure - Leases - Lease Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/LeasesLeaseCostsDetails</Role>
      <ShortName>Leases - Lease Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2414405 - Disclosure - Leases - Maturity Schedule Prior to the Adoptions of ASC 842 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/LeasesMaturitySchedulePriorToAdoptionsOfAsc842Details</Role>
      <ShortName>Leases - Maturity Schedule Prior to the Adoptions of ASC 842 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2415401 - Disclosure - Related Party Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/RelatedPartyTransactionsDetails</Role>
      <ShortName>Related Party Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/RelatedPartyTransactions</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - Quarterly Financial Data (unaudited) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.acceleronpharma.com/role/QuarterlyFinancialDataUnauditedDetails</Role>
      <ShortName>Quarterly Financial Data (unaudited) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.acceleronpharma.com/role/QuarterlyFinancialDataUnauditedTables</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="xlrn-20191231x10k.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items - xlrn-20191231x10k.htm</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/role/uncategorizedFacts</Role>
      <ShortName>Uncategorized Items - xlrn-20191231x10k.htm</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-K" original="xlrn-20191231x10k.htm">xlrn-20191231x10k.htm</File>
    <File>xlrn-20191231.xsd</File>
    <File>xlrn-20191231_cal.xml</File>
    <File>xlrn-20191231_def.xml</File>
    <File>xlrn-20191231_lab.xml</File>
    <File>xlrn-20191231_pre.xml</File>
    <File>xlrn-20191231xex1019.htm</File>
    <File>xlrn-20191231xex1021.htm</File>
    <File>xlrn-20191231xex1022.htm</File>
    <File>xlrn-20191231xex211.htm</File>
    <File>xlrn-20191231xex231.htm</File>
    <File>xlrn-20191231xex311.htm</File>
    <File>xlrn-20191231xex312.htm</File>
    <File>xlrn-20191231xex321.htm</File>
    <File>xlrn-20191231xex44.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>pipeline2020a01.jpg</File>
    <File>totalreturnchart2019.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
