<?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-20201013.xsd" xlink:type="simple"/>
    <context id="i087b54554c7941afa11bb71b96b69633_D20200810-20200810">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001370053</identifier>
        </entity>
        <period>
            <startDate>2020-08-10</startDate>
            <endDate>2020-08-10</endDate>
        </period>
    </context>
    <context id="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001370053</identifier>
        </entity>
        <period>
            <startDate>2020-10-13</startDate>
            <endDate>2020-10-13</endDate>
        </period>
    </context>
    <dei:EntityCentralIndexKey
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF80L2ZyYWc6YjUwZWU0YzQ0YTUyNDNhNWJkNzdiNjI3NmZkZDA4NWMvdGFibGU6OTA4YzRkMWM2NjI1NDg5OTg5ZDkyYjg1MGJkNDIxYTEvdGFibGVyYW5nZTo5MDhjNGQxYzY2MjU0ODk5ODlkOTJiODUwYmQ0MjFhMV8yLTEtMS0xLTA_3cb03e51-5d05-4119-aabe-fbbe31987282">0001370053</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="i087b54554c7941afa11bb71b96b69633_D20200810-20200810"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF80L2ZyYWc6YjUwZWU0YzQ0YTUyNDNhNWJkNzdiNjI3NmZkZDA4NWMvdGFibGU6OTA4YzRkMWM2NjI1NDg5OTg5ZDkyYjg1MGJkNDIxYTEvdGFibGVyYW5nZTo5MDhjNGQxYzY2MjU0ODk5ODlkOTJiODUwYmQ0MjFhMV81LTEtMS0xLTA_1037bfec-762a-470f-91ad-fd71eb1fc816">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="i087b54554c7941afa11bb71b96b69633_D20200810-20200810"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzY3_81451fda-fe1b-40c6-8f74-451ef39ebcd5">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xOTE_6b8069df-45de-4df9-bc56-d3cb64be369c">2020-10-13</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzYw_960e711b-4e0c-4c31-a5b6-32d8b3aea2cb">ANAPTYSBIO, INC</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6ZGY0ODMwZTEzMTVkNDNkM2EwMzE1ZDhjYmFkMDgxMWMvdGFibGVyYW5nZTpkZjQ4MzBlMTMxNWQ0M2QzYTAzMTVkOGNiYWQwODExY18wLTAtMS0xLTA_5a8eebf3-0903-401f-b21e-46bb76fc521a">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6ZGY0ODMwZTEzMTVkNDNkM2EwMzE1ZDhjYmFkMDgxMWMvdGFibGVyYW5nZTpkZjQ4MzBlMTMxNWQ0M2QzYTAzMTVkOGNiYWQwODExY18wLTEtMS0xLTA_c142cb08-c021-480d-a938-85d5cb243847">001-37985</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6ZGY0ODMwZTEzMTVkNDNkM2EwMzE1ZDhjYmFkMDgxMWMvdGFibGVyYW5nZTpkZjQ4MzBlMTMxNWQ0M2QzYTAzMTVkOGNiYWQwODExY18wLTItMS0xLTA_6c5d95f2-753f-486d-9d72-07c471d8ac98">20-3828755</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzYx_f868fddb-1aff-4f85-8717-4bdb8fdb11af">10421 Pacific Center Court</dei:EntityAddressAddressLine1>
    <dei:EntityAddressAddressLine2
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzU1_71bb5e9c-1fad-48b5-9ab0-96b89f1e0025">Suite 200</dei:EntityAddressAddressLine2>
    <dei:EntityAddressCityOrTown
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzU2_f438894e-9830-432f-960c-6503aea600e9">San Diego</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzU3_8304739b-7cdd-4bc5-9eb4-33e610270937">CA</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzU4_025d1ba0-cde0-400e-86b4-332c7a012971">92121</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzYy_94a64218-9011-470a-8d81-090c6e1e7ca5">858</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzY0_c94deb26-4af7-4a25-946c-1453cc34ed3c">362-6295</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzY4_25cb0fd5-cbd4-4e9e-8463-42ab40087197">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzYz_354eb7a2-b521-496c-a011-d32283c3d9f5">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzU5_df813600-a6b6-4320-931d-0dda27d8ab1a">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzY1_e11b0c82-348c-4a65-849e-357cd2d44bc5">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6MWU2ZmQ3NzM2MzY3NDg5MDlkNjgyZGIxNGI0OTA3NTgvdGFibGVyYW5nZToxZTZmZDc3MzYzNjc0ODkwOWQ2ODJkYjE0YjQ5MDc1OF8xLTAtMS0xLTA_ca703d4c-8992-4323-9f67-6df275648836">Common Stock, par value $0.001 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6MWU2ZmQ3NzM2MzY3NDg5MDlkNjgyZGIxNGI0OTA3NTgvdGFibGVyYW5nZToxZTZmZDc3MzYzNjc0ODkwOWQ2ODJkYjE0YjQ5MDc1OF8xLTEtMS0xLTA_9574662e-47b1-4ae4-8235-3b687e1e7368">ANAB</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGFibGU6MWU2ZmQ3NzM2MzY3NDg5MDlkNjgyZGIxNGI0OTA3NTgvdGFibGVyYW5nZToxZTZmZDc3MzYzNjc0ODkwOWQ2ODJkYjE0YjQ5MDc1OF8xLTItMS0xLTA_f953b664-9855-4cef-9205-254485e1abc2">NASDAQ</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="i2887b56cd12c42e1850d8b32eabf9aed_D20201013-20201013"
      id="id3VybDovL2RvY3MudjEvZG9jOjUxYjZmMzE5ZmY4ODQwZTQ4ZDdmMGYyNzg1NGI0NWUwL3NlYzo1MWI2ZjMxOWZmODg0MGU0OGQ3ZjBmMjc4NTRiNDVlMF8xL2ZyYWc6MjRjMTc0YzA4YzJkNDU1Yjk1NDgxNzE0YTI5OGU4NGMvdGV4dHJlZ2lvbjoyNGMxNzRjMDhjMmQ0NTViOTU0ODE3MTRhMjk4ZTg0Y18xNzY2_92f6b291-3ddd-4929-b496-277e6937c308">false</dei:EntityEmergingGrowthCompany>
</xbrl>
