<?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/2019-01-31"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="anab-20201104.xsd" xlink:type="simple"/>
    <context id="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001370053</identifier>
        </entity>
        <period>
            <startDate>2020-11-04</startDate>
            <endDate>2020-11-04</endDate>
        </period>
    </context>
    <dei:EntityCentralIndexKey
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF80L2ZyYWc6Y2RiYmZhOGYyMzZiNDM4YWI5ZTRlYjE4MmU1YjVkMjcvdGFibGU6NDhhM2U4MjVjY2NhNDA4ZmE0NDg0NWNjY2JkMDU1MTMvdGFibGVyYW5nZTo0OGEzZTgyNWNjY2E0MDhmYTQ0ODQ1Y2NjYmQwNTUxM18yLTEtMS0xLTA_afd335ec-a499-4e51-a7a6-1b8928f77e6d">0001370053</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF80L2ZyYWc6Y2RiYmZhOGYyMzZiNDM4YWI5ZTRlYjE4MmU1YjVkMjcvdGFibGU6NDhhM2U4MjVjY2NhNDA4ZmE0NDg0NWNjY2JkMDU1MTMvdGFibGVyYW5nZTo0OGEzZTgyNWNjY2E0MDhmYTQ0ODQ1Y2NjYmQwNTUxM181LTEtMS0xLTA_5d0eb848-08aa-4d67-9fe3-be9838b6ba13">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzYx_0136f558-acf8-4e0a-a159-1183a33f65b3">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xOTE_4ba91317-8167-405c-b548-3b9f1c2eee85">2020-11-04</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzU1_d67142b1-db8f-489c-aad6-d10565b1588c">ANAPTYSBIO, INC</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ZWNjMzBmMDAyYzQ0NGE1MzkyZTBhZDZhYmQxOTQyZDAvdGFibGVyYW5nZTplY2MzMGYwMDJjNDQ0YTUzOTJlMGFkNmFiZDE5NDJkMF8wLTAtMS0xLTA_fe11f026-591c-40c0-a30f-19a8612aa3d2">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ZWNjMzBmMDAyYzQ0NGE1MzkyZTBhZDZhYmQxOTQyZDAvdGFibGVyYW5nZTplY2MzMGYwMDJjNDQ0YTUzOTJlMGFkNmFiZDE5NDJkMF8wLTEtMS0xLTA_ee9018c4-3672-4a81-8f26-b4bef2de1b54">001-37985</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ZWNjMzBmMDAyYzQ0NGE1MzkyZTBhZDZhYmQxOTQyZDAvdGFibGVyYW5nZTplY2MzMGYwMDJjNDQ0YTUzOTJlMGFkNmFiZDE5NDJkMF8wLTItMS0xLTA_e3acb5f4-e66d-4125-8da7-30f6d2368702">20-3828755</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzYy_1dc0b2d3-86d4-4ab9-9bbc-7a57a71c8626">10421 Pacific Center Court</dei:EntityAddressAddressLine1>
    <dei:EntityAddressAddressLine2
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzYz_2e8966da-5527-4683-970d-61b818fcb208">Suite 200</dei:EntityAddressAddressLine2>
    <dei:EntityAddressCityOrTown
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY3_6b2fdc8f-e70f-4e4a-8eda-2530e70d4e89">San Diego</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY4_26d512ba-a702-4c66-945a-2e175352fa1b">CA</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY0_a091fbae-6517-45ab-b7c7-3c22a3a323bf">92121</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzU2_80852e53-32b0-4c0f-a89e-ede24c3dfce4">858</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY1_298618ff-f5e0-4973-a2f3-a85551beb9df">362-6295</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY5_ca779ca9-4293-46fb-899d-2410ae406822">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzcw_9ccabc7d-707b-40f7-b9fc-f969d9b54c1b">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzU3_9643eee8-1370-43f2-85df-366f99bc3080">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzU4_f8a24a89-461b-47e1-95d5-c0d0a5c0c1e3">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ODkyMDA4YjJlZmNhNGU1NWE1NTcyOGZmYjhlYmE1MGYvdGFibGVyYW5nZTo4OTIwMDhiMmVmY2E0ZTU1YTU1NzI4ZmZiOGViYTUwZl8xLTAtMS0xLTA_f59a5b12-0a08-46ca-b83b-9efad7939134">Common Stock, par value $0.001 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ODkyMDA4YjJlZmNhNGU1NWE1NTcyOGZmYjhlYmE1MGYvdGFibGVyYW5nZTo4OTIwMDhiMmVmY2E0ZTU1YTU1NzI4ZmZiOGViYTUwZl8xLTEtMS0xLTA_a588cee6-d5dc-4eed-9116-9cc5044cc5b8">ANAB</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGFibGU6ODkyMDA4YjJlZmNhNGU1NWE1NTcyOGZmYjhlYmE1MGYvdGFibGVyYW5nZTo4OTIwMDhiMmVmY2E0ZTU1YTU1NzI4ZmZiOGViYTUwZl8xLTItMS0xLTA_20419aa8-5c63-4963-b594-5fb028b2283f">NASDAQ</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF8xL2ZyYWc6YjE4OTk1MjRhNWRjNGUzZGE2YzQyNDJmZmUwNTBlZWUvdGV4dHJlZ2lvbjpiMTg5OTUyNGE1ZGM0ZTNkYTZjNDI0MmZmZTA1MGVlZV8xNzY2_022ddf05-f1ba-4b5e-ae1e-3b12cfa57f34">false</dei:EntityEmergingGrowthCompany>
    <dei:DocumentPeriodEndDate
      contextRef="i76c0a02b5cd74070971778ad20ae5c76_D20201104-20201104"
      id="id3VybDovL2RvY3MudjEvZG9jOmVjY2EyNWQ3MjQxMjRmZThiMTEyYmVhNWVkN2QzNGU4L3NlYzplY2NhMjVkNzI0MTI0ZmU4YjExMmJlYTVlZDdkMzRlOF83L2ZyYWc6ZTZjMzUwNzdkYTMyNGE3OTkyOTViNmMyYzIwMzRmZTcvdGFibGU6ODZjODNiZTNjMzE4NGQ2OGFhODkwN2MwZTMwN2E2ZjcvdGFibGVyYW5nZTo4NmM4M2JlM2MzMTg0ZDY4YWE4OTA3YzBlMzA3YTZmN18xLTAtMS0xLTgvdGV4dHJlZ2lvbjpmODgwOTQwOGVhOTU0YTAyODg5NjJiM2Q4MjgxODYzZV8xMDk5NTExNjI3ODIw_4ba91317-8167-405c-b548-3b9f1c2eee85">2020-11-04</dei:DocumentPeriodEndDate>
</xbrl>
