<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-04-30</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000701374</issuerCik>
        <issuerName>SIX FLAGS, INC.</issuerName>
        <issuerTradingSymbol>SXFL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001491618</rptOwnerCik>
            <rptOwnerName>BHR Master Fund, Ltd.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BHR CAPITAL, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>375 PARK AVENUE, 20TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10152</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001491617</rptOwnerCik>
            <rptOwnerName>BHR Capital, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>375 PARK AVENUE, 20TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10152</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001042288</rptOwnerCik>
            <rptOwnerName>VAN DYKE STEVEN A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>375 PARK AVENUE, 20TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10152</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.025 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2760048</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.025 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>287806</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These securities are held directly by BHR Master Fund, Ltd. (the &quot;Fund&quot;).  BHR Capital LLC (&quot;BHR&quot;) acts as investment advisor to the Fund, and shares voting and investment control with respect to these securities with the Fund.  Steven A. Van Dyke (&quot;Mr. Van Dyke&quot;) is the Chief Investment Officer of BHR, and controls the voting and investment decisions of BHR.  BHR and Mr. Van Dyke each disclaim beneficial ownership of these shares except to the extent of any pecuniary interest therein and this filing should not be deemed an admission of beneficial ownership for Section 16 purposes or any other purpose.</footnote>
        <footnote id="F2">These securities are owned solely by Mr. Van Dyke.  Mr. Van Dyke also serves a Managing Principal of Bay Harbour Management, L.C., an investment advisor registered under the Investment Advisers Act of 1940 (&quot;Bay Harbour&quot;).  Bay Harbour advises certain investment accounts that hold an additional 1,046,016 shares of the common stock of the Issuer, representing approximately 4.2% of the Issuer's outstanding common stock.  Bay Harbour and Mr. Van Dyke each disclaim beneficial ownership of the shares held by such accounts except to the extent of any pecuniary interest therein and this filing should not be deemed an admission of beneficial ownership for Section 16 purposes or any other purpose.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Steven A. Van Dyke - as Chief Investment Officer of the Investment Manager of BHR Master Fund, Ltd.</signatureName>
        <signatureDate>2010-05-10</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Steven A. Van Dyke - as Chief Investment Officer of BHR Capital, LLC</signatureName>
        <signatureDate>2010-05-10</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Steven A. Van Dyke</signatureName>
        <signatureDate>2010-05-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
