<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.7.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>137</ContextCount>
  <ElementCount>249</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>45</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>101 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DocumentandEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>103 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfFinancialPositionClassified</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>104 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfFinancialPositionClassifiedParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>105 - Statement - Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfIncomeAlternative</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>106 - Statement - Consolidated Statements of Operations and Comprehensive Loss (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfIncomeAlternativeParenthetical</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>107 - Statement - Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfShareholdersEquityAndOtherComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>108 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/StatementOfCashFlowsIndirect</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>109 - Disclosure - Background</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsOrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock</Role>
      <ShortName>Background</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>110 - Disclosure - Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock</Role>
      <ShortName>Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>111 - Disclosure - Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlock</Role>
      <ShortName>Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>112 - Disclosure - Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsFinancialInstrumentsDisclosureTextBlock</Role>
      <ShortName>Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>113 - Disclosure - Collaborative Arrangements and Revenue Recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsCollaborativeArrangementDisclosureTextBlock</Role>
      <ShortName>Collaborative Arrangements and Revenue Recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>114 - Disclosure - Capitalization and Warrant Liability</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlock</Role>
      <ShortName>Capitalization and Warrant Liability</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>115 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>116 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>117 - Disclosure - Profit Sharing Plan and 401(k) Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsCompensationAndEmployeeBenefitPlansTextBlock</Role>
      <ShortName>Profit Sharing Plan and 401(k) Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>118 - Disclosure - Subsequent and Other Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSubsequentEventsTextBlock</Role>
      <ShortName>Subsequent and Other Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>119 - Disclosure - Quarterly Financial Data (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsQuarterlyFinancialInformationTextBlock</Role>
      <ShortName>Quarterly Financial Data (unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>120 - Disclosure - Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockPolicies</Role>
      <ShortName>Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>121 - Disclosure - Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlockTables</Role>
      <ShortName>Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsSignificantAccountingPoliciesTextBlock</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>122 - Disclosure - Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlockTables</Role>
      <ShortName>Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsPropertyPlantAndEquipmentDisclosureTextBlock</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>123 - Disclosure - Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsFinancialInstrumentsDisclosureTextBlockTables</Role>
      <ShortName>Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsFinancialInstrumentsDisclosureTextBlock</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>124 - Disclosure - Capitalization and Warrant Liability (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlockTables</Role>
      <ShortName>Capitalization and Warrant Liability (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsStockholdersEquityNoteDisclosureTextBlock</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>125 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlockTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsDisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>126 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlockTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsIncomeTaxDisclosureTextBlock</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>127 - Disclosure - Quarterly Financial Data (unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsQuarterlyFinancialInformationTextBlockTables</Role>
      <ShortName>Quarterly Financial Data (unaudited) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.athersys.com/taxonomy/role/NotesToFinancialStatementsQuarterlyFinancialInformationTextBlock</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>128 - Disclosure - Background - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureBackgroundAdditionalInformation</Role>
      <ShortName>Background - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>129 - Disclosure - Accounting Policies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureAccountingPoliciesAdditionalInformation</Role>
      <ShortName>Accounting Policies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>130 - Disclosure - Accounting Policies - Fair Value of Stock-Based Compensation Awards (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureAccountingPoliciesFairValueOfStockBasedCompensationAwards</Role>
      <ShortName>Accounting Policies - Fair Value of Stock-Based Compensation Awards (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>131 - Disclosure - Accounting Policies - Net Loss and Number of Shares Used to Calculate Basic and Diluted Net Loss Per Share (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureAccountingPoliciesNetLossAndNumberOfSharesUsedToCalculateBasicAndDilutedNetLossPerShare</Role>
      <ShortName>Accounting Policies - Net Loss and Number of Shares Used to Calculate Basic and Diluted Net Loss Per Share (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>132 - Disclosure - Accounting Policies - Instruments Excluded from Calculation of Diluted Net Loss Per Share (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureAccountingPoliciesInstrumentsExcludedFromCalculationOfDilutedNetLossPerShare</Role>
      <ShortName>Accounting Policies - Instruments Excluded from Calculation of Diluted Net Loss Per Share (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>133 - Disclosure - Equipment - Equipment (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureEquipmentEquipment</Role>
      <ShortName>Equipment - Equipment (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>134 - Disclosure - Equipment - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureEquipmentAdditionalInformation</Role>
      <ShortName>Equipment - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>135 - Disclosure - Financial Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureFinancialInstrumentsSummaryOfFinancialAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasis</Role>
      <ShortName>Financial Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>136 - Disclosure - Financial Instruments - Fair Value of Warrants Based on Historical Volatilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureFinancialInstrumentsFairValueOfWarrantsBasedOnHistoricalVolatilities</Role>
      <ShortName>Financial Instruments - Fair Value of Warrants Based on Historical Volatilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>137 - Disclosure - Financial Instruments - Roll-Forward of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) for Warrants (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureFinancialInstrumentsRollForwardOfFairValueMeasurementsUsingSignificantUnobservableInputsLevel3ForWarrants</Role>
      <ShortName>Financial Instruments - Roll-Forward of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) for Warrants (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>138 - Disclosure - Financial Instruments - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureFinancialInstrumentsAdditionalInformation</Role>
      <ShortName>Financial Instruments - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>139 - Disclosure - Collaborative Arrangements and Revenue Recognition - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureCollaborativeArrangementsAndRevenueRecognitionAdditionalInformation</Role>
      <ShortName>Collaborative Arrangements and Revenue Recognition - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>140 - Disclosure - Capitalization and Warrant Liability - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureCapitalizationAndWarrantLiabilityAdditionalInformation</Role>
      <ShortName>Capitalization and Warrant Liability - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>141 - Disclosure - Capitalization and Warrant Liability - Common Stock Shares Reserved for Future Issuance (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureCapitalizationAndWarrantLiabilityCommonStockSharesReservedForFutureIssuance</Role>
      <ShortName>Capitalization and Warrant Liability - Common Stock Shares Reserved for Future Issuance (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>142 - Disclosure - Stock-Based Compensation - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformation</Role>
      <ShortName>Stock-Based Compensation - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>143 - Disclosure - Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockOptionActivityAndRelatedInformation</Role>
      <ShortName>Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>144 - Disclosure - Stock-Based Compensation - Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureStockBasedCompensationSummarizesInformationConcerningOptionsOutstandingAndOptionsVestedAndExercisable</Role>
      <ShortName>Stock-Based Compensation - Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>145 - Disclosure - Stock-Based Compensation - Summary of Restricted Stock Unit Activity and Related Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedStockUnitActivityAndRelatedInformation</Role>
      <ShortName>Stock-Based Compensation - Summary of Restricted Stock Unit Activity and Related Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>146 - Disclosure - Income Taxes - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureIncomeTaxesAdditionalInformation</Role>
      <ShortName>Income Taxes - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>147 - Disclosure - Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureIncomeTaxesScheduleOfReconciliationOfFederalStatutoryIncomeTaxRateToEffectiveTaxRate</Role>
      <ShortName>Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>148 - Disclosure - Income Taxes - Components of Deferred Tax Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureIncomeTaxesComponentsOfDeferredTaxAssets</Role>
      <ShortName>Income Taxes - Components of Deferred Tax Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>149 - Disclosure - Profit Sharing Plan and 401(k) Plan - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureProfitSharingPlanAnd401kPlanAdditionalInformation</Role>
      <ShortName>Profit Sharing Plan and 401(k) Plan - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>150 - Disclosure - Subsequent and Other Events - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureSubsequentAndOtherEventsAdditionalInformation</Role>
      <ShortName>Subsequent and Other Events - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="athx-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>151 - Disclosure - Quarterly Financial Data - Quarterly Financial Data (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.athersys.com/taxonomy/role/DisclosureQuarterlyFinancialDataQuarterlyFinancialData</Role>
      <ShortName>Quarterly Financial Data - Quarterly Financial Data (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>athx-20161231.xml</File>
    <File>athx-20161231.xsd</File>
    <File>athx-20161231_cal.xml</File>
    <File>athx-20161231_def.xml</File>
    <File>athx-20161231_lab.xml</File>
    <File>athx-20161231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
