<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xml:lang="en-US"
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2026"
  xmlns:ffd="http://xbrl.sec.gov/ffd/2026"
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  xmlns:xlink="http://www.w3.org/1999/xlink">
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      xlink:href="https://xbrl.sec.gov/ffd/2026/ffd-2026.xsd"
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        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001517413</identifier>
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        <period>
            <startDate>2026-08-06</startDate>
            <endDate>2026-08-06</endDate>
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    <context id="c-2">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001517413</identifier>
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                <xbrldi:typedMember dimension="ffd:OfferingAxis">
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        <period>
            <startDate>2026-08-06</startDate>
            <endDate>2026-08-06</endDate>
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    <context id="c-3">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001517413</identifier>
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                <xbrldi:typedMember dimension="ffd:OfferingAxis">
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        <period>
            <startDate>2026-08-06</startDate>
            <endDate>2026-08-06</endDate>
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    <context id="c-4">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001517413</identifier>
            <segment>
                <xbrldi:typedMember dimension="ffd:OfferingAxis">
                    <dei:lineNo>3</dei:lineNo>
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        <period>
            <startDate>2026-08-06</startDate>
            <endDate>2026-08-06</endDate>
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    <context id="c-5">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001517413</identifier>
            <segment>
                <xbrldi:typedMember dimension="ffd:OfferingAxis">
                    <dei:lineNo>4</dei:lineNo>
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        <period>
            <startDate>2026-08-06</startDate>
            <endDate>2026-08-06</endDate>
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    <unit id="usd">
        <measure>iso4217:USD</measure>
    </unit>
    <ffd:FeeExhibitTp contextRef="c-1" id="f-23">EX-FILING FEES</ffd:FeeExhibitTp>
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    <dei:EntityCentralIndexKey contextRef="c-1" id="f-25">0001517413</dei:EntityCentralIndexKey>
    <ffd:TtlFeeAmt contextRef="c-1" decimals="0" id="f-26" unitRef="usd">0</ffd:TtlFeeAmt>
    <ffd:OffsetTableNa contextRef="c-1" id="f-27">N/A</ffd:OffsetTableNa>
    <ffd:NetFeeAmt contextRef="c-1" decimals="0" id="f-28" unitRef="usd">0</ffd:NetFeeAmt>
    <ffd:CombinedProspectusTableNa contextRef="c-1" id="f-29">N/A</ffd:CombinedProspectusTableNa>
    <ffd:SubmissnTp contextRef="c-1" id="f-30">S-3ASR</ffd:SubmissnTp>
    <ffd:FormTp contextRef="c-1" id="f-1">S-3</ffd:FormTp>
    <dei:EntityRegistrantName contextRef="c-1" id="f-2">Fastly, Inc.</dei:EntityRegistrantName>
    <ffd:PrevslyPdFlg contextRef="c-2" id="f-3">false</ffd:PrevslyPdFlg>
    <ffd:PrevslyPdFlg contextRef="c-3" id="f-4">false</ffd:PrevslyPdFlg>
    <ffd:PrevslyPdFlg contextRef="c-4" id="f-5">false</ffd:PrevslyPdFlg>
    <ffd:PrevslyPdFlg contextRef="c-5" id="f-6">false</ffd:PrevslyPdFlg>
    <ffd:OfferingSctyTp contextRef="c-2" id="f-7">Debt</ffd:OfferingSctyTp>
    <ffd:OfferingSctyTitl contextRef="c-2" id="f-8">Debt Securities</ffd:OfferingSctyTitl>
    <ffd:Rule457rFlg contextRef="c-2" id="f-9">true</ffd:Rule457rFlg>
    <ffd:OfferingSctyTp contextRef="c-3" id="f-10">Equity</ffd:OfferingSctyTp>
    <ffd:OfferingSctyTitl contextRef="c-3" id="f-11">Preferred Stock, par value $0.00002 per share</ffd:OfferingSctyTitl>
    <ffd:Rule457rFlg contextRef="c-3" id="f-12">true</ffd:Rule457rFlg>
    <ffd:OfferingSctyTp contextRef="c-4" id="f-13">Equity</ffd:OfferingSctyTp>
    <ffd:OfferingSctyTitl contextRef="c-4" id="f-14">Class A Common Stock, par value $0.00002 per share</ffd:OfferingSctyTitl>
    <ffd:Rule457rFlg contextRef="c-4" id="f-15">true</ffd:Rule457rFlg>
    <ffd:OfferingSctyTp contextRef="c-5" id="f-16">Other</ffd:OfferingSctyTp>
    <ffd:OfferingSctyTitl contextRef="c-5" id="f-17">Warrants</ffd:OfferingSctyTitl>
    <ffd:Rule457rFlg contextRef="c-5" id="f-18">true</ffd:Rule457rFlg>
    <ffd:OfferingNote contextRef="c-5" id="f-22">&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;Separate consideration may or may not be received for securities that are issuable upon the conversion or exercise of, or in exchange for, other securities offered hereby.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;An unspecified aggregate initial offering price and number of securities of each identified class is being registered and may from time to time be offered at unspecified prices.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;The Registrant is relying on Rule 456(b) and Rule 457(r) under the Securities Act of 1933, as amended, to defer payment of all of the registration fees. In connection with the securities offered hereby, the Registrant will pay &#x201c;pay-as-you-go registration fees&#x201d; in accordance with Rule 456(b). The Registrant will calculate the registration fee applicable to an offer of securities pursuant to this Registration Statement based on the fee payment rate in effect on the date of such fee payment.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;Representing rights or obligations to purchase debt securities, preferred stock, Class A common stock or other securities, property or assets.&lt;/span&gt;</ffd:OfferingNote>
    <ffd:OfferingNote contextRef="c-4" id="f-21">&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;Separate consideration may or may not be received for securities that are issuable upon the conversion or exercise of, or in exchange for, other securities offered hereby.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;An unspecified aggregate initial offering price and number of securities of each identified class is being registered and may from time to time be offered at unspecified prices.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;The Registrant is relying on Rule 456(b) and Rule 457(r) under the Securities Act of 1933, as amended, to defer payment of all of the registration fees. In connection with the securities offered hereby, the Registrant will pay &#x201c;pay-as-you-go registration fees&#x201d; in accordance with Rule 456(b). The Registrant will calculate the registration fee applicable to an offer of securities pursuant to this Registration Statement based on the fee payment rate in effect on the date of such fee payment.&lt;/span&gt;</ffd:OfferingNote>
    <ffd:OfferingNote contextRef="c-3" id="f-20">&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;Separate consideration may or may not be received for securities that are issuable upon the conversion or exercise of, or in exchange for, other securities offered hereby.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;An unspecified aggregate initial offering price and number of securities of each identified class is being registered and may from time to time be offered at unspecified prices.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;The Registrant is relying on Rule 456(b) and Rule 457(r) under the Securities Act of 1933, as amended, to defer payment of all of the registration fees. In connection with the securities offered hereby, the Registrant will pay &#x201c;pay-as-you-go registration fees&#x201d; in accordance with Rule 456(b). The Registrant will calculate the registration fee applicable to an offer of securities pursuant to this Registration Statement based on the fee payment rate in effect on the date of such fee payment.&lt;/span&gt;</ffd:OfferingNote>
    <ffd:OfferingNote contextRef="c-2" id="f-19">&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;Separate consideration may or may not be received for securities that are issuable upon the conversion or exercise of, or in exchange for, other securities offered hereby.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;An unspecified aggregate initial offering price and number of securities of each identified class is being registered and may from time to time be offered at unspecified prices.&lt;/span&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:8.5pt;font-weight:400;line-height:100%"&gt;The Registrant is relying on Rule 456(b) and Rule 457(r) under the Securities Act of 1933, as amended, to defer payment of all of the registration fees. In connection with the securities offered hereby, the Registrant will pay &#x201c;pay-as-you-go registration fees&#x201d; in accordance with Rule 456(b). The Registrant will calculate the registration fee applicable to an offer of securities pursuant to this Registration Statement based on the fee payment rate in effect on the date of such fee payment.&lt;/span&gt;</ffd:OfferingNote>
</xbrl>
