{
 "instance": {
  "alec-10q_20210331.htm": {
   "axisCustom": 0,
   "axisStandard": 13,
   "contextCount": 70,
   "dts": {
    "calculationLink": {
     "local": [
      "alec-20210331_cal.xml"
     ]
    },
    "definitionLink": {
     "local": [
      "alec-20210331_def.xml"
     ],
     "remote": [
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-eedm-def-2020-01-31.xml",
      "http://xbrl.fasb.org/srt/2020/elts/srt-eedm1-def-2020-01-31.xml"
     ]
    },
    "inline": {
     "local": [
      "alec-10q_20210331.htm"
     ]
    },
    "labelLink": {
     "local": [
      "alec-20210331_lab.xml"
     ],
     "remote": [
      "https://xbrl.sec.gov/dei/2020/dei-doc-2020-01-31.xml",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-doc-2020-01-31.xml"
     ]
    },
    "presentationLink": {
     "local": [
      "alec-20210331_pre.xml"
     ]
    },
    "referenceLink": {
     "remote": [
      "https://xbrl.sec.gov/dei/2020/dei-ref-2020-01-31.xml",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-ref-2020-01-31.xml"
     ]
    },
    "schema": {
     "local": [
      "alec-20210331.xsd"
     ],
     "remote": [
      "http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xl-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xlink-2003-12-31.xsd",
      "http://www.xbrl.org/2005/xbrldt-2005.xsd",
      "https://xbrl.sec.gov/country/2020/country-2020-01-31.xsd",
      "http://www.xbrl.org/dtr/type/nonNumeric-2009-12-16.xsd",
      "https://xbrl.sec.gov/currency/2020/currency-2020-01-31.xsd",
      "https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd",
      "http://www.xbrl.org/dtr/type/numeric-2009-12-16.xsd",
      "https://xbrl.sec.gov/exch/2020/exch-2020-01-31.xsd",
      "http://www.xbrl.org/lrr/arcrole/factExplanatory-2009-12-16.xsd",
      "http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd",
      "http://www.xbrl.org/lrr/role/net-2009-12-16.xsd",
      "https://xbrl.sec.gov/naics/2017/naics-2017-01-31.xsd",
      "https://xbrl.sec.gov/sic/2020/sic-2020-01-31.xsd",
      "http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd",
      "http://www.xbrl.org/2006/ref-2006-02-27.xsd",
      "http://xbrl.fasb.org/srt/2020/elts/srt-types-2020-01-31.xsd",
      "http://xbrl.fasb.org/srt/2020/elts/srt-roles-2020-01-31.xsd",
      "https://xbrl.sec.gov/stpr/2018/stpr-2018-01-31.xsd",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-roles-2020-01-31.xsd",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-types-2020-01-31.xsd",
      "http://www.xbrl.org/lrr/role/deprecated-2009-12-16.xsd",
      "http://www.xbrl.org/lrr/role/reference-2009-12-16.xsd",
      "http://xbrl.fasb.org/us-gaap/2020/elts/us-parts-codification-2020-01-31.xsd"
     ]
    }
   },
   "elementCount": 272,
   "entityCount": 1,
   "hidden": {
    "http://fasb.org/us-gaap/2020-01-31": 6,
    "http://xbrl.sec.gov/dei/2020-01-31": 4,
    "total": 10
   },
   "keyCustom": 16,
   "keyStandard": 226,
   "memberCustom": 8,
   "memberStandard": 17,
   "nsprefix": "alec",
   "nsuri": "http://www.alector.com/20210331",
   "report": {
    "R1": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "dei:DocumentType",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "document",
     "isDefault": "true",
     "longName": "100000 - Document - Document and Entity Information",
     "role": "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation",
     "shortName": "Document and Entity Information",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "dei:DocumentType",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R10": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100090 - Disclosure - Fair Value Measurements",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurements",
     "shortName": "Fair Value Measurements",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R11": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100100 - Disclosure - Commitments and Contingencies",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingencies",
     "shortName": "Commitments and Contingencies",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R12": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100110 - Disclosure - Stock-based Compensation",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensation",
     "shortName": "Stock-based Compensation",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R13": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RelatedPartyTransactionsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100120 - Disclosure - Related Party Transactions",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactions",
     "shortName": "Related Party Transactions",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RelatedPartyTransactionsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R14": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100130 - Disclosure - Net Loss Per Share",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShare",
     "shortName": "Net Loss Per Share",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R15": {
     "firstAnchor": {
      "ancestors": [
       "us-gaap:SignificantAccountingPoliciesTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:BasisOfAccountingPolicyPolicyTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100140 - Disclosure - Summary of Significant Accounting Policies (Policies)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies",
     "shortName": "Summary of Significant Accounting Policies (Policies)",
     "subGroupType": "policies",
     "uniqueAnchor": {
      "ancestors": [
       "us-gaap:SignificantAccountingPoliciesTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:BasisOfAccountingPolicyPolicyTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R16": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfRestrictedCashAndCashEquivalentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100150 - Disclosure - Summary of Significant Accounting Policies (Tables)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables",
     "shortName": "Summary of Significant Accounting Policies (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfRestrictedCashAndCashEquivalentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R17": {
     "firstAnchor": {
      "ancestors": [
       "us-gaap:FairValueDisclosuresTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueAssetsMeasuredOnRecurringBasisTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100160 - Disclosure - Fair Value Measurements (Tables)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsTables",
     "shortName": "Fair Value Measurements (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "us-gaap:FairValueDisclosuresTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueAssetsMeasuredOnRecurringBasisTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R18": {
     "firstAnchor": {
      "ancestors": [
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100170 - Disclosure - Stock-based Compensation (Tables)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationTables",
     "shortName": "Stock-based Compensation (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R19": {
     "firstAnchor": {
      "ancestors": [
       "us-gaap:EarningsPerShareTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100180 - Disclosure - Net Loss Per Share (Tables)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareTables",
     "shortName": "Net Loss Per Share (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "us-gaap:EarningsPerShareTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R2": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:CashAndCashEquivalentsAtCarryingValue",
      "reportCount": 1,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100010 - Statement - Condensed Consolidated Balance Sheets (Unaudited)",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited",
     "shortName": "Condensed Consolidated Balance Sheets (Unaudited)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-3",
      "lang": null,
      "name": "us-gaap:MarketableSecuritiesCurrent",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R20": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "us-gaap:OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapSubsidiarySaleOfStockAxis_alecFollowOnPublicOfferingMember_20200130_20200130",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:StockIssuedDuringPeriodSharesNewIssues",
      "reportCount": 1,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100190 - Disclosure - The Company and Liquidity - Additional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails",
     "shortName": "The Company and Liquidity - Additional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "us-gaap:OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapSubsidiarySaleOfStockAxis_alecFollowOnPublicOfferingMember_20200130_20200130",
      "decimals": "-5",
      "lang": null,
      "name": "us-gaap:ProceedsFromIssuanceInitialPublicOffering",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R21": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "2",
      "first": true,
      "lang": null,
      "name": "alec:IncreaseInExpectedCostPercentage",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlipure",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100200 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails",
     "shortName": "Summary of Significant Accounting Policies - Additional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "2",
      "first": true,
      "lang": null,
      "name": "alec:IncreaseInExpectedCostPercentage",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlipure",
      "xsiNil": "false"
     }
    },
    "R22": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:CashAndCashEquivalentsAtCarryingValue",
      "reportCount": 1,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100210 - Disclosure - Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails",
     "shortName": "Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfRestrictedCashAndCashEquivalentsTextBlock",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20200331",
      "decimals": "-3",
      "lang": null,
      "name": "us-gaap:CashAndCashEquivalentsAtCarryingValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R23": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnRecurringBasisTextBlock",
       "us-gaap:FairValueDisclosuresTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapFairValueByAssetClassAxis_us-gaapMoneyMarketFundsMember_us-gaapFairValueByFairValueHierarchyLevelAxis_us-gaapFairValueInputsLevel1Member_us-gaapFairValueByMeasurementFrequencyAxis_us-gaapFairValueMeasurementsRecurringMember_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100220 - Disclosure - Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails",
     "shortName": "Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on a Recurring Basis (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnRecurringBasisTextBlock",
       "us-gaap:FairValueDisclosuresTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapFairValueByAssetClassAxis_us-gaapMoneyMarketFundsMember_us-gaapFairValueByFairValueHierarchyLevelAxis_us-gaapFairValueInputsLevel1Member_us-gaapFairValueByMeasurementFrequencyAxis_us-gaapFairValueMeasurementsRecurringMember_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R24": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-5",
      "first": true,
      "lang": null,
      "name": "us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100230 - Disclosure - Fair Value Measurements - Additional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails",
     "shortName": "Fair Value Measurements - Additional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-5",
      "first": true,
      "lang": null,
      "name": "us-gaap:AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R25": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-5",
      "first": true,
      "lang": null,
      "name": "us-gaap:FormerGainContingencyRecognizedInCurrentPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100240 - Disclosure - Commitment and Contingencies - Addtional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureCommitmentAndContingenciesAddtionalInformationDetails",
     "shortName": "Commitment and Contingencies - Addtional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "-5",
      "first": true,
      "lang": null,
      "name": "us-gaap:FormerGainContingencyRecognizedInCurrentPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R26": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:AllocatedShareBasedCompensationExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100250 - Disclosure - Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails",
     "shortName": "Stock-based Compensation - Summary of Recognized Stock-Based Compensation (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:AllocatedShareBasedCompensationExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R27": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapAwardTypeAxis_us-gaapRestrictedStockMember_20201231",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100260 - Disclosure - Stock-based Compensation - Summary of Restricted Common Stock (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails",
     "shortName": "Stock-based Compensation - Summary of Restricted Common Stock (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
       "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapAwardTypeAxis_us-gaapRestrictedStockMember_20201231",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     }
    },
    "R28": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapPlanNameAxis_alecTwoThousandNineteenEquityIncentivePlanMember_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100270 - Disclosure - Stock-based Compensation - Additional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
     "shortName": "Stock-based Compensation - Additional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapPlanNameAxis_alecTwoThousandNineteenEquityIncentivePlanMember_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R29": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapPlanNameAxis_alecTwoThousandNineteenEquityIncentivePlanMember_20201231",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100280 - Disclosure - Stock-based Compensation - Summary of Options to Purchase Common Stock (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails",
     "shortName": "Stock-based Compensation - Summary of Options to Purchase Common Stock (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapPlanNameAxis_alecTwoThousandNineteenEquityIncentivePlanMember_20201231",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     }
    },
    "R3": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:CommonStockParOrStatedValuePerShare",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100020 - Statement - Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited)",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParentheticalUnaudited",
     "shortName": "Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210331",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:CommonStockParOrStatedValuePerShare",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD_xbrlishares",
      "xsiNil": "false"
     }
    },
    "R30": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "us-gaap:OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapSubsidiarySaleOfStockAxis_alecFollowOnPublicOfferingMember_20200130_20200130",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:StockIssuedDuringPeriodSharesNewIssues",
      "reportCount": 1,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100290 - Disclosure - Related Party Transactions - Additional Information (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
     "shortName": "Related Party Transactions - Additional Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "us-gaap:RelatedPartyTransactionsDisclosureTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_us-gaapRelatedPartyTransactionsByRelatedPartyAxis_alecTwoThousandFourteenAdimabAgreementMember_20210101_20210331",
      "decimals": "-5",
      "lang": null,
      "name": "us-gaap:RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R31": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
       "us-gaap:EarningsPerShareTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100300 - Disclosure - Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details)",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails",
     "shortName": "Net Loss Per Share - Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
       "us-gaap:EarningsPerShareTextBlock",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "INF",
      "first": true,
      "lang": null,
      "name": "us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_xbrlishares",
      "xsiNil": "false"
     }
    },
    "R4": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100030 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited)",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited",
     "shortName": "Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R5": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20191231",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:StockholdersEquity",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100040 - Statement - Condensed Consolidated Statement of Stockholders' Equity",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity",
     "shortName": "Condensed Consolidated Statement of Stockholders' Equity",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20191231",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:StockholdersEquity",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R6": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20200101_20200331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "alec:IssuanceCostsOfCommonStock",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100050 - Statement - Condensed Consolidated Statement of Stockholders' Equity (Parenthetical)",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquityParenthetical",
     "shortName": "Condensed Consolidated Statement of Stockholders' Equity (Parenthetical)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20200101_20200331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "alec:IssuanceCostsOfCommonStock",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R7": {
     "firstAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100060 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)",
     "role": "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited",
     "shortName": "Condensed Consolidated Statements of Cash Flows (Unaudited)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "p",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": "-3",
      "first": true,
      "lang": null,
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unique": true,
      "unitRef": "U_iso4217USD",
      "xsiNil": "false"
     }
    },
    "R8": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100070 - Disclosure - The Company and Liquidity",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidity",
     "shortName": "The Company and Liquidity",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R9": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SignificantAccountingPoliciesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "100080 - Disclosure - Summary of Significant Accounting Policies",
     "role": "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies",
     "shortName": "Summary of Significant Accounting Policies",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "alec-10q_20210331.htm",
      "contextRef": "C_0001653087_20210101_20210331",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SignificantAccountingPoliciesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    }
   },
   "segmentCount": 27,
   "tag": {
    "alec_AbbVieBiotechnologyLimitedMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "AbbVie biotechnology, limited.",
        "label": "Abb Vie Biotechnology Limited [Member]",
        "terseLabel": "AbbVie Biotechnology Limited"
       }
      }
     },
     "localname": "AbbVieBiotechnologyLimitedMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_AccruedClinicalSupplyCost": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10120.0,
       "parentTag": "us-gaap_LiabilitiesCurrent",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accrued clinical supply cost.",
        "label": "Accrued Clinical Supply Cost",
        "terseLabel": "Accrued clinical supply costs"
       }
      }
     },
     "localname": "AccruedClinicalSupplyCost",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_AdimabMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Adimab [Member]",
        "terseLabel": "Adimab"
       }
      }
     },
     "localname": "AdimabMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_AmortizationRightOfUseAsset": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10130.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortization right of use asset.",
        "label": "Amortization Right Of Use Asset",
        "terseLabel": "Amortization of right-of-use assets"
       }
      }
     },
     "localname": "AmortizationRightOfUseAsset",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_AvailableForSaleSecuritiesDebtMaturitiesWithinOneThroughTwoYearFairValue": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Available For Sale Securities Debt Maturities Within One Through Two Year Fair Value.",
        "label": "Available For Sale Securities Debt Maturities Within One Through Two Year Fair Value",
        "terseLabel": "Remaining contractual maturities of investments were less than one year through two years"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesWithinOneThroughTwoYearFairValue",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_CashEquivalentsAndMarketableSecuritiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cash equivalents and marketable securities.",
        "label": "Cash Equivalents And Marketable Securities [Member]",
        "terseLabel": "Cash Equivalents and Marketable Securities"
       }
      }
     },
     "localname": "CashEquivalentsAndMarketableSecuritiesMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_CollaborativeArrangementAdditionalMilestonePaymentsReceivablePerProgram": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Collaborative arrangement, additional milestone payments receivable per program.",
        "label": "Collaborative Arrangement Additional Milestone Payments Receivable Per Program",
        "terseLabel": "Additional milestone payments per program related to initiation of certain clinical studies and regulatory approval"
       }
      }
     },
     "localname": "CollaborativeArrangementAdditionalMilestonePaymentsReceivablePerProgram",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_CollaborativeArrangementMilestonePaymentsOnOptionRightsExercisedPerProgram": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Collaborative arrangement, milestone payments on option rights exercised per program.",
        "label": "Collaborative Arrangement Milestone Payments On Option Rights Exercised Per Program",
        "terseLabel": "Exclusive option rights exercised for each program"
       }
      }
     },
     "localname": "CollaborativeArrangementMilestonePaymentsOnOptionRightsExercisedPerProgram",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_CollaborativeArrangementUpfrontPayments": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Collaborative arrangement, upfront payments.",
        "label": "Collaborative Arrangement Upfront Payments",
        "terseLabel": "Upfront payments"
       }
      }
     },
     "localname": "CollaborativeArrangementUpfrontPayments",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_DeferredOfferingCostsForPublicOfferingsIncludedInAccountsPayableAndAccruedLiabilities": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred offering costs for public offerings included in accounts payable and accrued liabilities.",
        "label": "Deferred Offering Costs For Public Offerings Included In Accounts Payable And Accrued Liabilities",
        "terseLabel": "Deferred offering costs in accounts payable and accrued liabilities"
       }
      }
     },
     "localname": "DeferredOfferingCostsForPublicOfferingsIncludedInAccountsPayableAndAccruedLiabilities",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_DevelopmentMilestone": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Development milestone.",
        "label": "Development Milestone",
        "terseLabel": "Development milestone"
       }
      }
     },
     "localname": "DevelopmentMilestone",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_FollowOnPublicOfferingMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Follow On Public Offering [Member]",
        "label": "Follow On Public Offering [Member]",
        "terseLabel": "Follow-on-offering"
       }
      }
     },
     "localname": "FollowOnPublicOfferingMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_FutureMilestonePaymentsOwed": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Future milestone payments owed.",
        "label": "Future Milestone Payments Owed",
        "terseLabel": "Future milestone payments owed"
       }
      }
     },
     "localname": "FutureMilestonePaymentsOwed",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_IncreaseDecreaseInAccruedLiabilitiesAndAccruedClinicalSupplyCosts": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10180.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase Decrease in accrued liabilities and accrued clinical supply costs.",
        "label": "Increase Decrease In Accrued Liabilities And Accrued Clinical Supply Costs",
        "terseLabel": "Accrued liabilities and accrued clinical supply costs"
       }
      }
     },
     "localname": "IncreaseDecreaseInAccruedLiabilitiesAndAccruedClinicalSupplyCosts",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_IncreaseDecreaseInLeaseLiabilities": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10200.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase (decrease) in lease liabilities.",
        "label": "Increase Decrease In Lease Liabilities",
        "terseLabel": "Lease liabilities"
       }
      }
     },
     "localname": "IncreaseDecreaseInLeaseLiabilities",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_IncreaseInExpectedCostPercentage": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase In Expected Cost Percentage.",
        "label": "Increase In Expected Cost Percentage",
        "terseLabel": "Increase in expected cost percentage"
       }
      }
     },
     "localname": "IncreaseInExpectedCostPercentage",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "alec_InnoventBiologicsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Innovent Biologics.",
        "label": "Innovent Biologics [Member]",
        "verboseLabel": "Innovent"
       }
      }
     },
     "localname": "InnoventBiologicsMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_IssuanceCostsOfCommonStock": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Issuance cost of common stock.",
        "label": "Issuance Costs Of Common Stock",
        "terseLabel": "Issuance cost of common stock"
       }
      }
     },
     "localname": "IssuanceCostsOfCommonStock",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquityParenthetical"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Organization consolidation and presentation of financial statements disclosure line items.",
        "label": "Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]",
        "terseLabel": "Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]"
       }
      }
     },
     "localname": "OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureLineItems",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "alec_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Organization consolidation and presentation of financial statements disclosure table.",
        "label": "Organization Consolidation And Presentation Of Financial Statements Disclosure [Table]",
        "terseLabel": "Organization Consolidation And Presentation Of Financial Statements Disclosure [Table]"
       }
      }
     },
     "localname": "OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTable",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "alec_ProceedsFromIssuanceOfCommonStockUponFollowOnPublicOfferingNetOfIssuanceCosts": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10040.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Proceeds from issuance of common stock upon follow-on public offering, net of issuance costs.",
        "label": "Proceeds From Issuance Of Common Stock Upon Follow On Public Offering Net Of Issuance Costs",
        "terseLabel": "Proceeds from issuance of common stock upon follow-on public offering, net of issuance costs"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfCommonStockUponFollowOnPublicOfferingNetOfIssuanceCosts",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_SalesMilestone": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sales milestone.",
        "label": "Sales Milestone",
        "terseLabel": "Sales milestone"
       }
      }
     },
     "localname": "SalesMilestone",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "alec_SubsequentOfferingPeriod": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Subsequent offering period.",
        "label": "Subsequent Offering Period",
        "terseLabel": "Subsequent offering period"
       }
      }
     },
     "localname": "SubsequentOfferingPeriod",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "alec_SummaryOfSignificantAccountingPoliciesLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Summary of significant accounting policies.",
        "label": "Summary Of Significant Accounting Policies [Line Items]",
        "terseLabel": "Summary Of Significant Accounting Policies [Line Items]"
       }
      }
     },
     "localname": "SummaryOfSignificantAccountingPoliciesLineItems",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "alec_SummaryOfSignificantAccountingPoliciesTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Summary of significant accounting policies.",
        "label": "Summary Of Significant Accounting Policies [Table]",
        "terseLabel": "Summary Of Significant Accounting Policies [Table]"
       }
      }
     },
     "localname": "SummaryOfSignificantAccountingPoliciesTable",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "alec_TwoThousandFourteenAdimabAgreementMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Adimab Agreement",
        "label": "Two Thousand Fourteen Adimab Agreement [Member]",
        "terseLabel": "Two Thousand Fourteen Adimab Agreement"
       }
      }
     },
     "localname": "TwoThousandFourteenAdimabAgreementMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_TwoThousandNineteenEmployeeStockPurchasePlanMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Two thousand nineteen employee stock purchase plan.",
        "label": "Two Thousand Nineteen Employee Stock Purchase Plan [Member]",
        "terseLabel": "2019 Employee Stock Purchase Plan"
       }
      }
     },
     "localname": "TwoThousandNineteenEmployeeStockPurchasePlanMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "alec_TwoThousandNineteenEquityIncentivePlanMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Two thousand nineteen equity incentive plan.",
        "label": "Two Thousand Nineteen Equity Incentive Plan [Member]",
        "terseLabel": "2019 Equity Incentive Plan"
       }
      }
     },
     "localname": "TwoThousandNineteenEquityIncentivePlanMember",
     "nsuri": "http://www.alector.com/20210331",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "dei_AmendmentFlag": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.",
        "label": "Amendment Flag",
        "terseLabel": "Amendment Flag"
       }
      }
     },
     "localname": "AmendmentFlag",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_CityAreaCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Area code of city",
        "label": "City Area Code",
        "terseLabel": "City Area Code"
       }
      }
     },
     "localname": "CityAreaCode",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_CoverAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cover page.",
        "label": "Cover [Abstract]"
       }
      }
     },
     "localname": "CoverAbstract",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "dei_CurrentFiscalYearEndDate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "End date of current fiscal year in the format --MM-DD.",
        "label": "Current Fiscal Year End Date",
        "terseLabel": "Current Fiscal Year End Date"
       }
      }
     },
     "localname": "CurrentFiscalYearEndDate",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "gMonthDayItemType"
    },
    "dei_DocumentFiscalPeriodFocus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fiscal period values are FY, Q1, Q2, and Q3.  1st, 2nd and 3rd quarter 10-Q or 10-QT statements have value Q1, Q2, and Q3 respectively, with 10-K, 10-KT or other fiscal year statements having FY.",
        "label": "Document Fiscal Period Focus",
        "terseLabel": "Document Fiscal Period Focus"
       }
      }
     },
     "localname": "DocumentFiscalPeriodFocus",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "fiscalPeriodItemType"
    },
    "dei_DocumentFiscalYearFocus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This is focus fiscal year of the document report in YYYY format. For a 2006 annual report, which may also provide financial information from prior periods, fiscal 2006 should be given as the fiscal year focus. Example: 2006.",
        "label": "Document Fiscal Year Focus",
        "terseLabel": "Document Fiscal Year Focus"
       }
      }
     },
     "localname": "DocumentFiscalYearFocus",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "gYearItemType"
    },
    "dei_DocumentPeriodEndDate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented.  If there is no historical data in the report, use the filing date. The format of the date is YYYY-MM-DD.",
        "label": "Document Period End Date",
        "terseLabel": "Document Period End Date"
       }
      }
     },
     "localname": "DocumentPeriodEndDate",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "dateItemType"
    },
    "dei_DocumentQuarterlyReport": {
     "auth_ref": [
      "r295"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true only for a form used as an quarterly report.",
        "label": "Document Quarterly Report",
        "terseLabel": "Document Quarterly Report"
       }
      }
     },
     "localname": "DocumentQuarterlyReport",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_DocumentTransitionReport": {
     "auth_ref": [
      "r296"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true only for a form used as a transition report.",
        "label": "Document Transition Report",
        "terseLabel": "Document Transition Report"
       }
      }
     },
     "localname": "DocumentTransitionReport",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_DocumentType": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.",
        "label": "Document Type",
        "terseLabel": "Document Type"
       }
      }
     },
     "localname": "DocumentType",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "submissionTypeItemType"
    },
    "dei_EntityAddressAddressLine1": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Address Line 1 such as Attn, Building Name, Street Name",
        "label": "Entity Address Address Line1",
        "terseLabel": "Entity Address, Address Line One"
       }
      }
     },
     "localname": "EntityAddressAddressLine1",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressAddressLine2": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Address Line 2 such as Street or Suite number",
        "label": "Entity Address Address Line2",
        "terseLabel": "Entity Address, Address Line Two"
       }
      }
     },
     "localname": "EntityAddressAddressLine2",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressCityOrTown": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the City or Town",
        "label": "Entity Address City Or Town",
        "terseLabel": "Entity Address, City or Town"
       }
      }
     },
     "localname": "EntityAddressCityOrTown",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressPostalZipCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Code for the postal or zip code",
        "label": "Entity Address Postal Zip Code",
        "terseLabel": "Entity Address, Postal Zip Code"
       }
      }
     },
     "localname": "EntityAddressPostalZipCode",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressStateOrProvince": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the state or province.",
        "label": "Entity Address State Or Province",
        "terseLabel": "Entity Address, State or Province"
       }
      }
     },
     "localname": "EntityAddressStateOrProvince",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "stateOrProvinceItemType"
    },
    "dei_EntityCentralIndexKey": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.",
        "label": "Entity Central Index Key",
        "terseLabel": "Entity Central Index Key"
       }
      }
     },
     "localname": "EntityCentralIndexKey",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "centralIndexKeyItemType"
    },
    "dei_EntityCommonStockSharesOutstanding": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate number of shares or other units outstanding of each of registrant's classes of capital or common stock or other ownership interests, if and as stated on cover of related periodic report. Where multiple classes or units exist define each class/interest by adding class of stock items such as Common Class A [Member], Common Class B [Member] or Partnership Interest [Member] onto the Instrument [Domain] of the Entity Listings, Instrument.",
        "label": "Entity Common Stock Shares Outstanding",
        "terseLabel": "Entity Common Stock, Shares Outstanding"
       }
      }
     },
     "localname": "EntityCommonStockSharesOutstanding",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "sharesItemType"
    },
    "dei_EntityCurrentReportingStatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate 'Yes' or 'No' whether registrants (1) have filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that registrants were required to file such reports), and (2) have been subject to such filing requirements for the past 90 days. This information should be based on the registrant's current or most recent filing containing the related disclosure.",
        "label": "Entity Current Reporting Status",
        "terseLabel": "Entity Current Reporting Status"
       }
      }
     },
     "localname": "EntityCurrentReportingStatus",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_EntityEmergingGrowthCompany": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate if registrant meets the emerging growth company criteria.",
        "label": "Entity Emerging Growth Company",
        "terseLabel": "Entity Emerging Growth Company"
       }
      }
     },
     "localname": "EntityEmergingGrowthCompany",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntityFileNumber": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.",
        "label": "Entity File Number",
        "terseLabel": "Entity File Number"
       }
      }
     },
     "localname": "EntityFileNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "fileNumberItemType"
    },
    "dei_EntityFilerCategory": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate whether the registrant is one of the following: Large Accelerated Filer, Accelerated Filer, Non-accelerated Filer. Definitions of these categories are stated in Rule 12b-2 of the Exchange Act. This information should be based on the registrant's current or most recent filing containing the related disclosure.",
        "label": "Entity Filer Category",
        "terseLabel": "Entity Filer Category"
       }
      }
     },
     "localname": "EntityFilerCategory",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "filerCategoryItemType"
    },
    "dei_EntityIncorporationStateCountryCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Two-character EDGAR code representing the state or country of incorporation.",
        "label": "Entity Incorporation State Country Code",
        "terseLabel": "Entity Incorporation, State or Country Code"
       }
      }
     },
     "localname": "EntityIncorporationStateCountryCode",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "edgarStateCountryItemType"
    },
    "dei_EntityInteractiveDataCurrent": {
     "auth_ref": [
      "r298"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).",
        "label": "Entity Interactive Data Current",
        "terseLabel": "Entity Interactive Data Current"
       }
      }
     },
     "localname": "EntityInteractiveDataCurrent",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_EntityRegistrantName": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.",
        "label": "Entity Registrant Name",
        "terseLabel": "Entity Registrant Name"
       }
      }
     },
     "localname": "EntityRegistrantName",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityShellCompany": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the registrant is a shell company as defined in Rule 12b-2 of the Exchange Act.",
        "label": "Entity Shell Company",
        "terseLabel": "Entity Shell Company"
       }
      }
     },
     "localname": "EntityShellCompany",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntitySmallBusiness": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicates that the company is a Smaller Reporting Company (SRC).",
        "label": "Entity Small Business",
        "terseLabel": "Entity Small Business"
       }
      }
     },
     "localname": "EntitySmallBusiness",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntityTaxIdentificationNumber": {
     "auth_ref": [
      "r297"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.",
        "label": "Entity Tax Identification Number",
        "terseLabel": "Entity Tax Identification Number"
       }
      }
     },
     "localname": "EntityTaxIdentificationNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "employerIdItemType"
    },
    "dei_LocalPhoneNumber": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Local phone number for entity.",
        "label": "Local Phone Number",
        "terseLabel": "Local Phone Number"
       }
      }
     },
     "localname": "LocalPhoneNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_Security12bTitle": {
     "auth_ref": [
      "r293"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Title of a 12(b) registered security.",
        "label": "Security12b Title",
        "terseLabel": "Title of 12(b) Security"
       }
      }
     },
     "localname": "Security12bTitle",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "securityTitleItemType"
    },
    "dei_SecurityExchangeName": {
     "auth_ref": [
      "r294"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the Exchange on which a security is registered.",
        "label": "Security Exchange Name",
        "terseLabel": "Security Exchange Name"
       }
      }
     },
     "localname": "SecurityExchangeName",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "edgarExchangeCodeItemType"
    },
    "dei_TradingSymbol": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Trading symbol of an instrument as listed on an exchange.",
        "label": "Trading Symbol",
        "terseLabel": "Trading Symbol"
       }
      }
     },
     "localname": "TradingSymbol",
     "nsuri": "http://xbrl.sec.gov/dei/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation"
     ],
     "xbrltype": "tradingSymbolItemType"
    },
    "srt_CounterpartyNameAxis": {
     "auth_ref": [
      "r32",
      "r70"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Counterparty Name [Axis]",
        "terseLabel": "Counterparty Name"
       }
      }
     },
     "localname": "CounterpartyNameAxis",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_DirectorMember": {
     "auth_ref": [
      "r116"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Director [Member]",
        "terseLabel": "Director"
       }
      }
     },
     "localname": "DirectorMember",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_MaximumMember": {
     "auth_ref": [
      "r163",
      "r164",
      "r246",
      "r247",
      "r248",
      "r249",
      "r250",
      "r251",
      "r252",
      "r283",
      "r284"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Maximum [Member]",
        "terseLabel": "Maximum"
       }
      }
     },
     "localname": "MaximumMember",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_MinimumMember": {
     "auth_ref": [
      "r163",
      "r164",
      "r246",
      "r247",
      "r248",
      "r249",
      "r250",
      "r251",
      "r252",
      "r283",
      "r284"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Minimum [Member]",
        "terseLabel": "Minimum [Member]"
       }
      }
     },
     "localname": "MinimumMember",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_RangeAxis": {
     "auth_ref": [
      "r153",
      "r163",
      "r164",
      "r246",
      "r247",
      "r248",
      "r249",
      "r250",
      "r251",
      "r252",
      "r283",
      "r284"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Range [Axis]",
        "terseLabel": "Statistical Measurement"
       }
      }
     },
     "localname": "RangeAxis",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_RangeMember": {
     "auth_ref": [
      "r153",
      "r163",
      "r164",
      "r246",
      "r247",
      "r248",
      "r249",
      "r250",
      "r251",
      "r252",
      "r283",
      "r284"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Range [Member]",
        "terseLabel": "Statistical Measurement"
       }
      }
     },
     "localname": "RangeMember",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_RepurchaseAgreementCounterpartyNameDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Repurchase Agreement Counterparty Name [Domain]",
        "terseLabel": "Counterparty Name"
       }
      }
     },
     "localname": "RepurchaseAgreementCounterpartyNameDomain",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_TitleOfIndividualAxis": {
     "auth_ref": [
      "r116",
      "r239"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Title Of Individual [Axis]",
        "terseLabel": "Title of Individual"
       }
      }
     },
     "localname": "TitleOfIndividualAxis",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_TitleOfIndividualWithRelationshipToEntityDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Title Of Individual With Relationship To Entity [Domain]",
        "terseLabel": "Title of Individual"
       }
      }
     },
     "localname": "TitleOfIndividualWithRelationshipToEntityDomain",
     "nsuri": "http://fasb.org/srt/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AccountingPoliciesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Accounting Policies [Abstract]"
       }
      }
     },
     "localname": "AccountingPoliciesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccountsPayableCurrent": {
     "auth_ref": [
      "r23"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10110.0,
       "parentTag": "us-gaap_LiabilitiesCurrent",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).",
        "label": "Accounts Payable Current",
        "terseLabel": "Accounts payable"
       }
      }
     },
     "localname": "AccountsPayableCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments": {
     "auth_ref": [
      "r59"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10120.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.",
        "label": "Accretion Amortization Of Discounts And Premiums Investments",
        "negatedLabel": "Amortization of premiums and accretion of discounts on marketable securities"
       }
      }
     },
     "localname": "AccretionAmortizationOfDiscountsAndPremiumsInvestments",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccruedLiabilitiesCurrent": {
     "auth_ref": [
      "r26"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10130.0,
       "parentTag": "us-gaap_LiabilitiesCurrent",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).",
        "label": "Accrued Liabilities Current",
        "terseLabel": "Accrued liabilities"
       }
      }
     },
     "localname": "AccruedLiabilitiesCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax": {
     "auth_ref": [
      "r15",
      "r36",
      "r37",
      "r38",
      "r277",
      "r289",
      "r290"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10050.0,
       "parentTag": "us-gaap_StockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.",
        "label": "Accumulated Other Comprehensive Income Loss Net Of Tax",
        "terseLabel": "Accumulated other comprehensive income"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeLossNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeMember": {
     "auth_ref": [
      "r35",
      "r38",
      "r39",
      "r73",
      "r74",
      "r75",
      "r207",
      "r285",
      "r286"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accumulated increase (decrease) in equity from transactions and other events and circumstances from non-owner sources, attributable to the parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners.",
        "label": "Accumulated Other Comprehensive Income [Member]",
        "terseLabel": "Accumulated Other Comprehensive Income"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AdditionalPaidInCapital": {
     "auth_ref": [
      "r13",
      "r192"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10040.0,
       "parentTag": "us-gaap_StockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.",
        "label": "Additional Paid In Capital",
        "terseLabel": "Additional paid-in capital"
       }
      }
     },
     "localname": "AdditionalPaidInCapital",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AdditionalPaidInCapitalMember": {
     "auth_ref": [
      "r73",
      "r74",
      "r75",
      "r189",
      "r190",
      "r191"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders.",
        "label": "Additional Paid In Capital [Member]",
        "terseLabel": "Additional Paid-In Capital"
       }
      }
     },
     "localname": "AdditionalPaidInCapitalMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue": {
     "auth_ref": [
      "r165",
      "r167",
      "r194",
      "r195"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase to additional paid-in capital (APIC) for recognition of cost for award under share-based payment arrangement.",
        "label": "Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value",
        "terseLabel": "Stock-based compensation"
       }
      }
     },
     "localname": "AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract]",
        "terseLabel": "Adjustments to reconcile net loss to net cash used in operating activities:"
       }
      }
     },
     "localname": "AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AllocatedShareBasedCompensationExpense": {
     "auth_ref": [
      "r167",
      "r185",
      "r193"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.",
        "label": "Allocated Share Based Compensation Expense",
        "terseLabel": "Total stock-based compensation"
       }
      }
     },
     "localname": "AllocatedShareBasedCompensationExpense",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.",
        "label": "Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount",
        "terseLabel": "Anti-dilutive shares"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of antidilutive security.",
        "label": "Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis]",
        "terseLabel": "Antidilutive Securities"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]",
        "terseLabel": "Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AntidilutiveSecuritiesNameDomain": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Incremental common shares attributable to securities that were not included in diluted earnings per share (EPS) because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.",
        "label": "Antidilutive Securities Name [Domain]",
        "terseLabel": "Antidilutive Securities, Name"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_Assets": {
     "auth_ref": [
      "r68",
      "r102",
      "r105",
      "r111",
      "r124",
      "r202",
      "r208",
      "r224",
      "r267",
      "r275"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.",
        "label": "Assets",
        "totalLabel": "Total assets"
       }
      }
     },
     "localname": "Assets",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AssetsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Assets [Abstract]",
        "terseLabel": "Assets"
       }
      }
     },
     "localname": "AssetsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AssetsCurrent": {
     "auth_ref": [
      "r4",
      "r5",
      "r31",
      "r68",
      "r124",
      "r202",
      "r208",
      "r224"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10160.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.",
        "label": "Assets Current",
        "totalLabel": "Total current assets"
       }
      }
     },
     "localname": "AssetsCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AssetsCurrentAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Assets Current [Abstract]",
        "terseLabel": "Current assets:"
       }
      }
     },
     "localname": "AssetsCurrentAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AssetsFairValueDisclosure": {
     "auth_ref": [
      "r213"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails": {
       "order": 10030.0,
       "parentTag": "us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.",
        "label": "Assets Fair Value Disclosure",
        "terseLabel": "Cash equivalents and marketable securities, Fair Market Value"
       }
      }
     },
     "localname": "AssetsFairValueDisclosure",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax": {
     "auth_ref": [
      "r120"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails": {
       "order": 10010.0,
       "parentTag": "us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax",
        "terseLabel": "Cash equivalents and marketable securities, Unrealized Gains"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax": {
     "auth_ref": [
      "r121"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails": {
       "order": 10020.0,
       "parentTag": "us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax",
        "negatedLabel": "Cash equivalents and marketable securities, Unrealized Losses"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis": {
     "auth_ref": [
      "r119",
      "r126"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Available For Sale Debt Securities Amortized Cost Basis",
        "totalLabel": "Cash equivalents and marketable securities, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue": {
     "auth_ref": [
      "r122",
      "r123",
      "r273"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Available For Sale Securities Debt Maturities Within One Year Fair Value",
        "terseLabel": "Remaining contractual maturities of investments were less than one year"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AwardTypeAxis": {
     "auth_ref": [
      "r168",
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of award under share-based payment arrangement.",
        "label": "Award Type [Axis]",
        "terseLabel": "Award Type"
       }
      }
     },
     "localname": "AwardTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_BasisOfAccountingPolicyPolicyTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for basis of accounting, or basis of presentation, used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS).",
        "label": "Basis Of Accounting Policy Policy [Text Block]",
        "terseLabel": "Basis of Presentation"
       }
      }
     },
     "localname": "BasisOfAccountingPolicyPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_CapitalExpendituresIncurredButNotYetPaid": {
     "auth_ref": [
      "r62",
      "r63",
      "r64"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Future cash outflow to pay for purchases of fixed assets that have occurred.",
        "label": "Capital Expenditures Incurred But Not Yet Paid",
        "terseLabel": "Property and equipment purchases included in accounts payable and accrued liabilities"
       }
      }
     },
     "localname": "CapitalExpendituresIncurredButNotYetPaid",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashAndCashEquivalentsAtCarryingValue": {
     "auth_ref": [
      "r2",
      "r21",
      "r60"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails": {
       "order": 10010.0,
       "parentTag": "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents",
       "weight": 1.0
      },
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10210.0,
       "parentTag": "us-gaap_AssetsCurrent",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.",
        "label": "Cash And Cash Equivalents At Carrying Value",
        "terseLabel": "Cash and cash equivalents"
       }
      }
     },
     "localname": "CashAndCashEquivalentsAtCarryingValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashAndCashEquivalentsAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of cash and cash equivalent balance.",
        "label": "Cash And Cash Equivalents [Axis]",
        "terseLabel": "Cash and Cash Equivalents"
       }
      }
     },
     "localname": "CashAndCashEquivalentsAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy": {
     "auth_ref": [
      "r7",
      "r61",
      "r66",
      "r266"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Entity's cash and cash equivalents accounting policy with respect to restricted balances.  Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits.",
        "label": "Cash And Cash Equivalents Restricted Cash And Cash Equivalents Policy",
        "terseLabel": "Cash, Cash Equivalents, and Restricted Cash"
       }
      }
     },
     "localname": "CashAndCashEquivalentsRestrictedCashAndCashEquivalentsPolicy",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents": {
     "auth_ref": [
      "r54",
      "r60",
      "r65"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.",
        "label": "Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents",
        "periodEndLabel": "Cash, cash equivalents, and restricted cash at end of period",
        "periodStartLabel": "Cash, cash equivalents, and restricted cash at beginning of period",
        "totalLabel": "Total cash, cash equivalents, and restricted cash"
       }
      }
     },
     "localname": "CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]"
       }
      }
     },
     "localname": "CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect": {
     "auth_ref": [
      "r54",
      "r225"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in cash, cash equivalents, and cash and cash equivalents restricted to withdrawal or usage; including effect from exchange rate change. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.",
        "label": "Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect",
        "totalLabel": "Net increase in cash, cash equivalents, and restricted cash"
       }
      }
     },
     "localname": "CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Cash Flow Noncash Investing And Financing Activities Disclosure [Abstract]",
        "terseLabel": "Non-cash investing and financing activities:"
       }
      }
     },
     "localname": "CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_CommitmentsAndContingenciesDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Commitments And Contingencies Disclosure [Abstract]"
       }
      }
     },
     "localname": "CommitmentsAndContingenciesDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_CommitmentsAndContingenciesDisclosureTextBlock": {
     "auth_ref": [
      "r130",
      "r131",
      "r132",
      "r134"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for commitments and contingencies.",
        "label": "Commitments And Contingencies Disclosure [Text Block]",
        "terseLabel": "Commitments and Contingencies"
       }
      }
     },
     "localname": "CommitmentsAndContingenciesDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingencies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_CommonStockCapitalSharesReservedForFutureIssuance": {
     "auth_ref": [
      "r29"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate number of common shares reserved for future issuance.",
        "label": "Common Stock Capital Shares Reserved For Future Issuance",
        "terseLabel": "Common stock reserved for issuance"
       }
      }
     },
     "localname": "CommonStockCapitalSharesReservedForFutureIssuance",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockMember": {
     "auth_ref": [
      "r73",
      "r74"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Stock that is subordinate to all other stock of the issuer.",
        "label": "Common Stock [Member]",
        "terseLabel": "Common Stock"
       }
      }
     },
     "localname": "CommonStockMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommonStockParOrStatedValuePerShare": {
     "auth_ref": [
      "r12"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Face amount or stated value per share of common stock.",
        "label": "Common Stock Par Or Stated Value Per Share",
        "terseLabel": "Common stock, par value"
       }
      }
     },
     "localname": "CommonStockParOrStatedValuePerShare",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParentheticalUnaudited"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_CommonStockSharesAuthorized": {
     "auth_ref": [
      "r12"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The maximum number of common shares permitted to be issued by an entity's charter and bylaws.",
        "label": "Common Stock Shares Authorized",
        "terseLabel": "Common stock, shares authorized"
       }
      }
     },
     "localname": "CommonStockSharesAuthorized",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParentheticalUnaudited"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockSharesIssued": {
     "auth_ref": [
      "r12"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.",
        "label": "Common Stock Shares Issued",
        "terseLabel": "Common stock, shares issued"
       }
      }
     },
     "localname": "CommonStockSharesIssued",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParentheticalUnaudited"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockSharesOutstanding": {
     "auth_ref": [
      "r12",
      "r135"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.",
        "label": "Common Stock Shares Outstanding",
        "periodEndLabel": "Ending balance (in shares)",
        "periodStartLabel": "Beginning balance (in shares)",
        "terseLabel": "Common stock, shares outstanding"
       }
      }
     },
     "localname": "CommonStockSharesOutstanding",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParentheticalUnaudited",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockValue": {
     "auth_ref": [
      "r12"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10030.0,
       "parentTag": "us-gaap_StockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity.",
        "label": "Common Stock Value",
        "terseLabel": "Common stock, $0.0001 par value; 200,000,000 shares authorized; 79,731,647 and 79,316,261 shares issued and outstanding as of March 31, 2021 and December 31, 2020"
       }
      }
     },
     "localname": "CommonStockValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ComprehensiveIncomeNetOfTax": {
     "auth_ref": [
      "r42",
      "r44",
      "r45",
      "r47",
      "r270",
      "r282"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.",
        "label": "Comprehensive Income Net Of Tax",
        "totalLabel": "Comprehensive loss"
       }
      }
     },
     "localname": "ComprehensiveIncomeNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ComprehensiveIncomePolicyPolicyTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for comprehensive income.",
        "label": "Comprehensive Income Policy Policy [Text Block]",
        "terseLabel": "Comprehensive Loss"
       }
      }
     },
     "localname": "ComprehensiveIncomePolicyPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ConcentrationRiskCreditRisk": {
     "auth_ref": [
      "r94",
      "r274"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for credit risk.",
        "label": "Concentration Risk Credit Risk",
        "terseLabel": "Concentration of Credit Risk"
       }
      }
     },
     "localname": "ConcentrationRiskCreditRisk",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ContractWithCustomerLiability": {
     "auth_ref": [
      "r137",
      "r138",
      "r150"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.",
        "label": "Contract With Customer Liability",
        "terseLabel": "Deferred revenue"
       }
      }
     },
     "localname": "ContractWithCustomerLiability",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice": {
     "auth_ref": [
      "r139"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in estimate of transaction price which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due. Includes, but is not limited to, change in assessment of whether estimate of variable consideration is constrained.",
        "label": "Contract With Customer Liability Cumulative Catch Up Adjustment To Revenue Change In Estimate Of Transaction Price",
        "terseLabel": "Reduced revenue"
       }
      }
     },
     "localname": "ContractWithCustomerLiabilityCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractWithCustomerLiabilityCurrent": {
     "auth_ref": [
      "r137",
      "r138",
      "r150"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10140.0,
       "parentTag": "us-gaap_LiabilitiesCurrent",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.",
        "label": "Contract With Customer Liability Current",
        "terseLabel": "Deferred revenue, current portion"
       }
      }
     },
     "localname": "ContractWithCustomerLiabilityCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractWithCustomerLiabilityNoncurrent": {
     "auth_ref": [
      "r137",
      "r138",
      "r150"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10080.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as noncurrent.",
        "label": "Contract With Customer Liability Noncurrent",
        "terseLabel": "Deferred revenue, long-term portion"
       }
      }
     },
     "localname": "ContractWithCustomerLiabilityNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractWithCustomerLiabilityRevenueRecognized": {
     "auth_ref": [
      "r151"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.",
        "label": "Contract With Customer Liability Revenue Recognized",
        "terseLabel": "Collaboration revenue"
       }
      }
     },
     "localname": "ContractWithCustomerLiabilityRevenueRecognized",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CorporateBondSecuritiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This category includes information about long-term debt securities that are issued by either a domestic or foreign corporate business entity with a date certain promise of repayment and a return to the holder for the time value of money (for example, variable or fixed interest, original issue discount).",
        "label": "Corporate Bond Securities [Member]",
        "terseLabel": "Corporate Bonds"
       }
      }
     },
     "localname": "CorporateBondSecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DepreciationAndAmortization": {
     "auth_ref": [
      "r58",
      "r127"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10100.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.",
        "label": "Depreciation And Amortization",
        "terseLabel": "Depreciation and amortization"
       }
      }
     },
     "localname": "DepreciationAndAmortization",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock": {
     "auth_ref": [
      "r196"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for share-based payment arrangement.",
        "label": "Disclosure Of Compensation Related Costs Share Based Payments [Text Block]",
        "terseLabel": "Stock-Based Compensation"
       }
      }
     },
     "localname": "DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensation"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]"
       }
      }
     },
     "localname": "DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_DueToRelatedPartiesCurrent": {
     "auth_ref": [
      "r23",
      "r71",
      "r237"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).",
        "label": "Due To Related Parties Current",
        "terseLabel": "Accrued liabilities due to related parties"
       }
      }
     },
     "localname": "DueToRelatedPartiesCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EarningsPerShareAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Earnings Per Share [Abstract]"
       }
      }
     },
     "localname": "EarningsPerShareAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_EarningsPerShareBasicAndDiluted": {
     "auth_ref": [
      "r86"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements.  Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period.  Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.",
        "label": "Earnings Per Share Basic And Diluted",
        "terseLabel": "Net loss per share, basic and diluted"
       }
      }
     },
     "localname": "EarningsPerShareBasicAndDiluted",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_EarningsPerShareTextBlock": {
     "auth_ref": [
      "r87",
      "r88",
      "r89",
      "r90"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for earnings per share.",
        "label": "Earnings Per Share [Text Block]",
        "terseLabel": "Net Loss Per Share"
       }
      }
     },
     "localname": "EarningsPerShareTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShare"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized": {
     "auth_ref": [
      "r186"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost not yet recognized for nonvested award under share-based payment arrangement.",
        "label": "Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized",
        "terseLabel": "Unrecognized stock-based compensation"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1": {
     "auth_ref": [
      "r186"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.",
        "label": "Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Period For Recognition1",
        "terseLabel": "Expected weighted average period"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions": {
     "auth_ref": [
      "r186"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost to be recognized for option under share-based payment arrangement.",
        "label": "Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized Stock Options",
        "terseLabel": "Unrecognized stock-based compensation"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EmployeeStockMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "An Employee Stock Purchase Plan is a tax-efficient means by which employees of a corporation can purchase the corporation's stock.",
        "label": "Employee Stock [Member]",
        "terseLabel": "Shares Committed Under 2019 ESPP"
       }
      }
     },
     "localname": "EmployeeStockMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EmployeeStockOptionMember": {
     "auth_ref": [
      "r183"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Share-based payment arrangement granting right, subject to vesting and other restrictions, to purchase or sell certain number of shares at predetermined price for specified period of time.",
        "label": "Employee Stock Option [Member]",
        "verboseLabel": "Options to Purchase Common Stock"
       }
      }
     },
     "localname": "EmployeeStockOptionMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EquityComponentDomain": {
     "auth_ref": [
      "r73",
      "r74",
      "r75",
      "r77",
      "r82",
      "r84",
      "r91",
      "r125",
      "r135",
      "r136",
      "r189",
      "r190",
      "r191",
      "r198",
      "r199",
      "r226",
      "r227",
      "r228",
      "r229",
      "r230",
      "r231",
      "r285",
      "r286",
      "r287"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Components of equity are the parts of the total Equity balance including that which is allocated to common, preferred, treasury stock, retained earnings, etc.",
        "label": "Equity Component [Domain]",
        "terseLabel": "Equity Component"
       }
      }
     },
     "localname": "EquityComponentDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]",
        "terseLabel": "Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]"
       }
      }
     },
     "localname": "FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable": {
     "auth_ref": [
      "r213",
      "r214",
      "r215",
      "r220"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about asset and liability measured at fair value on recurring and nonrecurring basis.",
        "label": "Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]",
        "terseLabel": "Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]"
       }
      }
     },
     "localname": "FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueAssetsMeasuredOnRecurringBasisTextBlock": {
     "auth_ref": [
      "r213",
      "r214"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).",
        "label": "Fair Value Assets Measured On Recurring Basis [Text Block]",
        "terseLabel": "Summary of Financial Assets Measured at Fair Value on a Recurring Basis"
       }
      }
     },
     "localname": "FairValueAssetsMeasuredOnRecurringBasisTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain": {
     "auth_ref": [
      "r218"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Class of asset.",
        "label": "Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation By Asset Class [Domain]",
        "terseLabel": "Asset Class"
       }
      }
     },
     "localname": "FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueByAssetClassAxis": {
     "auth_ref": [
      "r213",
      "r220"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by class of asset.",
        "label": "Fair Value By Asset Class [Axis]",
        "terseLabel": "Asset Class"
       }
      }
     },
     "localname": "FairValueByAssetClassAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByFairValueHierarchyLevelAxis": {
     "auth_ref": [
      "r154",
      "r155",
      "r156",
      "r157",
      "r158",
      "r159",
      "r160",
      "r162",
      "r214",
      "r243",
      "r244",
      "r245"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by level within fair value hierarchy and fair value measured at net asset value per share as practical expedient.",
        "label": "Fair Value By Fair Value Hierarchy Level [Axis]",
        "terseLabel": "Fair Value Hierarchy and NAV"
       }
      }
     },
     "localname": "FairValueByFairValueHierarchyLevelAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByMeasurementFrequencyAxis": {
     "auth_ref": [
      "r213",
      "r214",
      "r216",
      "r217",
      "r221"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by measurement frequency.",
        "label": "Fair Value By Measurement Frequency [Axis]",
        "terseLabel": "Fair Value, Measurements, Recurring"
       }
      }
     },
     "localname": "FairValueByMeasurementFrequencyAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueDisclosuresAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Fair Value Disclosures [Abstract]"
       }
      }
     },
     "localname": "FairValueDisclosuresAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueDisclosuresTextBlock": {
     "auth_ref": [
      "r219"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.",
        "label": "Fair Value Disclosures [Text Block]",
        "terseLabel": "Fair Value Measurements"
       }
      }
     },
     "localname": "FairValueDisclosuresTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurements"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueInputsLevel1Member": {
     "auth_ref": [
      "r154",
      "r155",
      "r160",
      "r162",
      "r214",
      "r243"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Quoted prices in active markets for identical assets or liabilities that the reporting entity can access at the measurement date.",
        "label": "Fair Value Inputs Level1 [Member]",
        "terseLabel": "Level 1"
       }
      }
     },
     "localname": "FairValueInputsLevel1Member",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueInputsLevel2Member": {
     "auth_ref": [
      "r154",
      "r155",
      "r160",
      "r162",
      "r214",
      "r244"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Inputs other than quoted prices included within level 1 that are observable for an asset or liability, either directly or indirectly, including, but not limited to, quoted prices for similar assets or liabilities in active markets, or quoted prices for identical or similar assets or liabilities in inactive markets.",
        "label": "Fair Value Inputs Level2 [Member]",
        "terseLabel": "Fair Value, Inputs, Level 2"
       }
      }
     },
     "localname": "FairValueInputsLevel2Member",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementFrequencyDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measurement frequency.",
        "label": "Fair Value Measurement Frequency [Domain]",
        "terseLabel": "Measurement Frequency"
       }
      }
     },
     "localname": "FairValueMeasurementFrequencyDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementsFairValueHierarchyDomain": {
     "auth_ref": [
      "r154",
      "r155",
      "r156",
      "r157",
      "r158",
      "r159",
      "r160",
      "r162",
      "r243",
      "r244",
      "r245"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Categories used to prioritize the inputs to valuation techniques to measure fair value.",
        "label": "Fair Value Measurements Fair Value Hierarchy [Domain]",
        "terseLabel": "Fair Value Hierarchy and NAV"
       }
      }
     },
     "localname": "FairValueMeasurementsFairValueHierarchyDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementsRecurringMember": {
     "auth_ref": [
      "r219",
      "r221"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Frequent fair value measurement. Includes, but is not limited to, fair value adjustment for impairment of asset, liability or equity, frequently measured at fair value.",
        "label": "Fair Value Measurements Recurring [Member]",
        "terseLabel": "Fair Value, Measurements, Recurring"
       }
      }
     },
     "localname": "FairValueMeasurementsRecurringMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueOfFinancialInstrumentsPolicy": {
     "auth_ref": [
      "r66",
      "r222",
      "r223"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for determining the fair value of financial instruments.",
        "label": "Fair Value Of Financial Instruments Policy",
        "terseLabel": "Fair Value of Financial Instruments"
       }
      }
     },
     "localname": "FairValueOfFinancialInstrumentsPolicy",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FormerGainContingencyRecognizedInCurrentPeriod": {
     "auth_ref": [
      "r133"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain recognized in the period that had been disclosed in prior periods as a contingent gain.",
        "label": "Former Gain Contingency Recognized In Current Period",
        "terseLabel": "Gain contingency, Recognized"
       }
      }
     },
     "localname": "FormerGainContingencyRecognizedInCurrentPeriod",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureCommitmentAndContingenciesAddtionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GainLossOnSaleOfPropertyPlantEquipment": {
     "auth_ref": [
      "r58"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10140.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.",
        "label": "Gain Loss On Sale Of Property Plant Equipment",
        "negatedLabel": "Loss from disposal of property and equipment, net"
       }
      }
     },
     "localname": "GainLossOnSaleOfPropertyPlantEquipment",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GeneralAndAdministrativeExpense": {
     "auth_ref": [
      "r49"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10080.0,
       "parentTag": "us-gaap_OperatingExpenses",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.",
        "label": "General And Administrative Expense",
        "terseLabel": "General and administrative"
       }
      }
     },
     "localname": "GeneralAndAdministrativeExpense",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GeneralAndAdministrativeExpenseMember": {
     "auth_ref": [
      "r48"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Primary financial statement caption encompassing general and administrative expense.",
        "label": "General And Administrative Expense [Member]",
        "verboseLabel": "General and Administrative"
       }
      }
     },
     "localname": "GeneralAndAdministrativeExpenseMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_IncomeStatementLocationAxis": {
     "auth_ref": [
      "r129"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by location in the income statement.",
        "label": "Income Statement Location [Axis]",
        "terseLabel": "Income Statement Location"
       }
      }
     },
     "localname": "IncomeStatementLocationAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncomeStatementLocationDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Location in the income statement.",
        "label": "Income Statement Location [Domain]",
        "terseLabel": "Income Statement Location"
       }
      }
     },
     "localname": "IncomeStatementLocationDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_IncreaseDecreaseInAccountsPayable": {
     "auth_ref": [
      "r57"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10170.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The increase (decrease) during the reporting period in the aggregate amount of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business.",
        "label": "Increase Decrease In Accounts Payable",
        "terseLabel": "Accounts payable"
       }
      }
     },
     "localname": "IncreaseDecreaseInAccountsPayable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInContractWithCustomerLiability": {
     "auth_ref": [
      "r57"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10190.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration has been received or is receivable.",
        "label": "Increase Decrease In Contract With Customer Liability",
        "terseLabel": "Deferred revenue"
       }
      }
     },
     "localname": "IncreaseDecreaseInContractWithCustomerLiability",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInOperatingCapitalAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Increase Decrease In Operating Capital [Abstract]",
        "terseLabel": "Changes in operating assets and liabilities:"
       }
      }
     },
     "localname": "IncreaseDecreaseInOperatingCapitalAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10210.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in noncurrent operating liabilities classified as other.",
        "label": "Increase Decrease In Other Noncurrent Liabilities",
        "terseLabel": "Other long-term liabilities"
       }
      }
     },
     "localname": "IncreaseDecreaseInOtherNoncurrentLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInOtherOperatingAssets": {
     "auth_ref": [
      "r57"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10160.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in operating assets classified as other.",
        "label": "Increase Decrease In Other Operating Assets",
        "negatedLabel": "Other assets"
       }
      }
     },
     "localname": "IncreaseDecreaseInOtherOperatingAssets",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets": {
     "auth_ref": [
      "r57"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10150.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in prepaid expenses, and assets classified as other.",
        "label": "Increase Decrease In Prepaid Deferred Expense And Other Assets",
        "negatedLabel": "Prepaid expenses and other current assets"
       }
      }
     },
     "localname": "IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_Liabilities": {
     "auth_ref": [
      "r24",
      "r68",
      "r106",
      "r124",
      "r203",
      "r208",
      "r209",
      "r224"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10010.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.",
        "label": "Liabilities",
        "totalLabel": "Total liabilities"
       }
      }
     },
     "localname": "Liabilities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LiabilitiesAndStockholdersEquity": {
     "auth_ref": [
      "r18",
      "r68",
      "r124",
      "r224",
      "r268",
      "r279"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of liabilities and equity items, including the portion of equity attributable to noncontrolling interests, if any.",
        "label": "Liabilities And Stockholders Equity",
        "totalLabel": "Total liabilities and stockholders\u2019 equity"
       }
      }
     },
     "localname": "LiabilitiesAndStockholdersEquity",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LiabilitiesAndStockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Liabilities And Stockholders Equity [Abstract]",
        "terseLabel": "Liabilities and stockholders\u2019 equity"
       }
      }
     },
     "localname": "LiabilitiesAndStockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LiabilitiesCurrent": {
     "auth_ref": [
      "r27",
      "r68",
      "r124",
      "r203",
      "r208",
      "r209",
      "r224"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10070.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer.",
        "label": "Liabilities Current",
        "totalLabel": "Total current liabilities"
       }
      }
     },
     "localname": "LiabilitiesCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LiabilitiesCurrentAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Liabilities Current [Abstract]",
        "terseLabel": "Current liabilities:"
       }
      }
     },
     "localname": "LiabilitiesCurrentAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_MarketableSecuritiesCurrent": {
     "auth_ref": [
      "r3",
      "r25"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10220.0,
       "parentTag": "us-gaap_AssetsCurrent",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in marketable security, classified as current.",
        "label": "Marketable Securities Current",
        "terseLabel": "Marketable securities"
       }
      }
     },
     "localname": "MarketableSecuritiesCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_MoneyMarketFundsMember": {
     "auth_ref": [
      "r154"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fund that invests in short-term money-market instruments, for example, but not limited to, commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and other highly liquid securities.",
        "label": "Money Market Funds [Member]",
        "terseLabel": "Money Market Funds"
       }
      }
     },
     "localname": "MoneyMarketFundsMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_NetCashProvidedByUsedInFinancingActivities": {
     "auth_ref": [
      "r54"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10030.0,
       "parentTag": "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.",
        "label": "Net Cash Provided By Used In Financing Activities",
        "totalLabel": "Net cash provided by financing activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInFinancingActivities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided By Used In Financing Activities [Abstract]",
        "terseLabel": "Cash flows from financing activities:"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInFinancingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetCashProvidedByUsedInInvestingActivities": {
     "auth_ref": [
      "r54"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10020.0,
       "parentTag": "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.",
        "label": "Net Cash Provided By Used In Investing Activities",
        "totalLabel": "Net cash provided by (used in) investing activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInInvestingActivities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided By Used In Investing Activities [Abstract]",
        "terseLabel": "Cash flows from investing activities:"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInInvestingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetCashProvidedByUsedInOperatingActivities": {
     "auth_ref": [
      "r54",
      "r56",
      "r59"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10010.0,
       "parentTag": "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect",
       "weight": 1.0
      }
     },
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.",
        "label": "Net Cash Provided By Used In Operating Activities",
        "totalLabel": "Net cash used in operating activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInOperatingActivities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided By Used In Operating Activities [Abstract]",
        "terseLabel": "Cash flows from operating activities:"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInOperatingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetIncomeLoss": {
     "auth_ref": [
      "r0",
      "r40",
      "r43",
      "r46",
      "r59",
      "r68",
      "r76",
      "r78",
      "r79",
      "r80",
      "r81",
      "r83",
      "r84",
      "r85",
      "r102",
      "r104",
      "r107",
      "r110",
      "r112",
      "r124",
      "r224",
      "r269",
      "r281"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10010.0,
       "parentTag": "us-gaap_ComprehensiveIncomeNetOfTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.",
        "label": "Net Income Loss",
        "terseLabel": "Net loss",
        "totalLabel": "Net loss"
       }
      }
     },
     "localname": "NetIncomeLoss",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingExpenses": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10060.0,
       "parentTag": "us-gaap_OperatingIncomeLoss",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.",
        "label": "Operating Expenses",
        "totalLabel": "Total operating expenses"
       }
      }
     },
     "localname": "OperatingExpenses",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingExpensesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Operating Expenses [Abstract]",
        "terseLabel": "Operating expenses:"
       }
      }
     },
     "localname": "OperatingExpensesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_OperatingIncomeLoss": {
     "auth_ref": [
      "r102",
      "r104",
      "r107",
      "r110",
      "r112"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10030.0,
       "parentTag": "us-gaap_NetIncomeLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net result for the period of deducting operating expenses from operating revenues.",
        "label": "Operating Income Loss",
        "totalLabel": "Loss from operations"
       }
      }
     },
     "localname": "OperatingIncomeLoss",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingLeaseLiabilityCurrent": {
     "auth_ref": [
      "r233"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10150.0,
       "parentTag": "us-gaap_LiabilitiesCurrent",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.",
        "label": "Operating Lease Liability Current",
        "terseLabel": "Operating lease liabilities, current portion"
       }
      }
     },
     "localname": "OperatingLeaseLiabilityCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingLeaseLiabilityNoncurrent": {
     "auth_ref": [
      "r233"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10090.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent.",
        "label": "Operating Lease Liability Noncurrent",
        "terseLabel": "Operating lease liabilities, long-term portion"
       }
      }
     },
     "localname": "OperatingLeaseLiabilityNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingLeaseRightOfUseAsset": {
     "auth_ref": [
      "r232"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10180.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's right to use underlying asset under operating lease.",
        "label": "Operating Lease Right Of Use Asset",
        "terseLabel": "Operating lease right-of-use assets"
       }
      }
     },
     "localname": "OperatingLeaseRightOfUseAsset",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Organization Consolidation And Presentation Of Financial Statements [Abstract]"
       }
      }
     },
     "localname": "OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock": {
     "auth_ref": [
      "r1",
      "r212"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.",
        "label": "Organization Consolidation And Presentation Of Financial Statements Disclosure [Text Block]",
        "terseLabel": "The Company and Liquidity"
       }
      }
     },
     "localname": "OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidity"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_OtherAssetsNoncurrent": {
     "auth_ref": [
      "r22"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10200.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of noncurrent assets classified as other.",
        "label": "Other Assets Noncurrent",
        "terseLabel": "Other assets"
       }
      }
     },
     "localname": "OtherAssetsNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax": {
     "auth_ref": [
      "r33",
      "r34"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10020.0,
       "parentTag": "us-gaap_ComprehensiveIncomeNetOfTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and before adjustment, of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.",
        "label": "Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Reclassification Adjustments Net Of Tax",
        "terseLabel": "Unrealized gain (loss) on marketable securities"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent": {
     "auth_ref": [
      "r41",
      "r44",
      "r200",
      "r201",
      "r206"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after tax of other comprehensive income (loss) attributable to parent entity.",
        "label": "Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent",
        "terseLabel": "Unrealized gain (loss) on marketable securities"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherLiabilitiesNoncurrent": {
     "auth_ref": [
      "r28"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10100.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer.",
        "label": "Other Liabilities Noncurrent",
        "terseLabel": "Other long-term liabilities"
       }
      }
     },
     "localname": "OtherLiabilitiesNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherNonoperatingIncomeExpense": {
     "auth_ref": [
      "r50"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10040.0,
       "parentTag": "us-gaap_NetIncomeLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of income (expense) related to nonoperating activities, classified as other.",
        "label": "Other Nonoperating Income Expense",
        "terseLabel": "Other income, net"
       }
      }
     },
     "localname": "OtherNonoperatingIncomeExpense",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OverAllotmentOptionMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Right given to the underwriter to sell additional shares over the initial allotment.",
        "label": "Over Allotment Option [Member]",
        "terseLabel": "Over-Allotment Option"
       }
      }
     },
     "localname": "OverAllotmentOptionMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PaymentsToAcquireMarketableSecurities": {
     "auth_ref": [
      "r118"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10070.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow for purchase of marketable security.",
        "label": "Payments To Acquire Marketable Securities",
        "negatedLabel": "Purchase of marketable securities"
       }
      }
     },
     "localname": "PaymentsToAcquireMarketableSecurities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsToAcquirePropertyPlantAndEquipment": {
     "auth_ref": [
      "r51"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10060.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.",
        "label": "Payments To Acquire Property Plant And Equipment",
        "negatedLabel": "Purchase of property and equipment"
       }
      }
     },
     "localname": "PaymentsToAcquirePropertyPlantAndEquipment",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PlanNameAxis": {
     "auth_ref": [
      "r168",
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by plan name for share-based payment arrangement.",
        "label": "Plan Name [Axis]",
        "terseLabel": "Plan Name"
       }
      }
     },
     "localname": "PlanNameAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_PlanNameDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Plan name for share-based payment arrangement.",
        "label": "Plan Name [Domain]",
        "terseLabel": "Plan Name"
       }
      }
     },
     "localname": "PlanNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PrepaidExpenseAndOtherAssetsCurrent": {
     "auth_ref": [
      "r4",
      "r19",
      "r20"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10230.0,
       "parentTag": "us-gaap_AssetsCurrent",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of asset related to consideration paid in advance for costs that provide economic benefits in future periods, and amount of other assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer.",
        "label": "Prepaid Expense And Other Assets Current",
        "terseLabel": "Prepaid expenses and other current assets"
       }
      }
     },
     "localname": "PrepaidExpenseAndOtherAssetsCurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromCollaborators": {
     "auth_ref": [
      "r55"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cash received from collaborators during the current period.",
        "label": "Proceeds From Collaborators",
        "terseLabel": "Upfront payment received"
       }
      }
     },
     "localname": "ProceedsFromCollaborators",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromIssuanceInitialPublicOffering": {
     "auth_ref": [
      "r52"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash inflow associated with the amount received from entity's first offering of stock to the public.",
        "label": "Proceeds From Issuance Initial Public Offering",
        "terseLabel": "Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses"
       }
      }
     },
     "localname": "ProceedsFromIssuanceInitialPublicOffering",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities": {
     "auth_ref": [],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10080.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities  (held-to-maturity or available-for-sale) during the period.",
        "label": "Proceeds From Sale And Maturity Of Marketable Securities",
        "terseLabel": "Maturities of marketable securities"
       }
      }
     },
     "localname": "ProceedsFromSaleAndMaturityOfMarketableSecurities",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromStockOptionsExercised": {
     "auth_ref": [
      "r52",
      "r188"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10050.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from exercise of option under share-based payment arrangement.",
        "label": "Proceeds From Stock Options Exercised",
        "terseLabel": "Proceeds from the exercise of options to purchase common stock"
       }
      }
     },
     "localname": "ProceedsFromStockOptionsExercised",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProfitLoss": {
     "auth_ref": [
      "r0",
      "r40",
      "r43",
      "r53",
      "r68",
      "r76",
      "r83",
      "r84",
      "r102",
      "r104",
      "r107",
      "r110",
      "r112",
      "r124",
      "r200",
      "r204",
      "r205",
      "r210",
      "r211",
      "r224",
      "r271"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10090.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.",
        "label": "Profit Loss",
        "terseLabel": "Net loss"
       }
      }
     },
     "localname": "ProfitLoss",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentNet": {
     "auth_ref": [
      "r8",
      "r9",
      "r128",
      "r280"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10170.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.",
        "label": "Property Plant And Equipment Net",
        "terseLabel": "Property and equipment, net"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentNet",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RelatedPartyDomain": {
     "auth_ref": [
      "r161",
      "r236",
      "r237"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Related parties include affiliates; other entities for which investments are accounted for by the equity method by the entity; trusts for benefit of employees; and principal owners, management, and members of immediate families. It also may include other parties with which the entity may control or can significantly influence the management or operating policies of the other to an extent that one of the transacting parties might be prevented from fully pursuing its own separate interests.",
        "label": "Related Party [Domain]",
        "terseLabel": "Related Party"
       }
      }
     },
     "localname": "RelatedPartyDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty": {
     "auth_ref": [
      "r236"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.",
        "label": "Related Party Transaction Expenses From Transactions With Related Party",
        "terseLabel": "Related party transaction expenses"
       }
      }
     },
     "localname": "RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RelatedPartyTransactionLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Related Party Transaction [Line Items]",
        "terseLabel": "Related Party Transaction [Line Items]"
       }
      }
     },
     "localname": "RelatedPartyTransactionLineItems",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_RelatedPartyTransactionsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Related Party Transactions [Abstract]"
       }
      }
     },
     "localname": "RelatedPartyTransactionsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_RelatedPartyTransactionsByRelatedPartyAxis": {
     "auth_ref": [
      "r161",
      "r236",
      "r240",
      "r254",
      "r255",
      "r256",
      "r257",
      "r258",
      "r259",
      "r260",
      "r261",
      "r262",
      "r263",
      "r264",
      "r265"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of related party. Related parties include, but not limited to, affiliates; other entities for which investments are accounted for by the equity method by the entity; trusts for benefit of employees; and principal owners, management, and members of immediate families. It also may include other parties with which the entity may control or can significantly influence the management or operating policies of the other to an extent that one of the transacting parties might be prevented from fully pursuing its own separate interests.",
        "label": "Related Party Transactions By Related Party [Axis]",
        "terseLabel": "Related Party"
       }
      }
     },
     "localname": "RelatedPartyTransactionsByRelatedPartyAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_RelatedPartyTransactionsDisclosureTextBlock": {
     "auth_ref": [
      "r234",
      "r235",
      "r237",
      "r241",
      "r242"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.",
        "label": "Related Party Transactions Disclosure [Text Block]",
        "terseLabel": "Related Party Transactions"
       }
      }
     },
     "localname": "RelatedPartyTransactionsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactions"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ResearchAndDevelopmentExpense": {
     "auth_ref": [
      "r197",
      "r292"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10070.0,
       "parentTag": "us-gaap_OperatingExpenses",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.",
        "label": "Research And Development Expense",
        "terseLabel": "Research and development"
       }
      }
     },
     "localname": "ResearchAndDevelopmentExpense",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ResearchAndDevelopmentExpenseMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Primary financial statement caption in which the reported facts about research and development expense have been included.",
        "label": "Research And Development Expense [Member]",
        "terseLabel": "Research and Development"
       }
      }
     },
     "localname": "ResearchAndDevelopmentExpenseMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Type of cash and cash equivalent. Cash is currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.",
        "label": "Restricted Cash And Cash Equivalents Cash And Cash Equivalents [Member]",
        "terseLabel": "Cash and Cash Equivalents"
       }
      }
     },
     "localname": "RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RestrictedCashNoncurrent": {
     "auth_ref": [
      "r6",
      "r10",
      "r65",
      "r291"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails": {
       "order": 10020.0,
       "parentTag": "us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents",
       "weight": 1.0
      },
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10190.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.",
        "label": "Restricted Cash Noncurrent",
        "terseLabel": "Restricted cash"
       }
      }
     },
     "localname": "RestrictedCashNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesReconciliationOfCashCashEquivalentsAndRestrictedCashDetails",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RestrictedStockMember": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Stock including a provision that prohibits sale or substantive sale of an equity instrument for a specified period of time or until specified performance conditions are met.",
        "label": "Restricted Stock [Member]",
        "terseLabel": "Restricted Common Stock"
       }
      }
     },
     "localname": "RestrictedStockMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RetainedEarningsAccumulatedDeficit": {
     "auth_ref": [
      "r14",
      "r136",
      "r192",
      "r278",
      "r288",
      "r290"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10060.0,
       "parentTag": "us-gaap_StockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cumulative amount of the reporting entity's undistributed earnings or deficit.",
        "label": "Retained Earnings Accumulated Deficit",
        "terseLabel": "Accumulated deficit"
       }
      }
     },
     "localname": "RetainedEarningsAccumulatedDeficit",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RetainedEarningsMember": {
     "auth_ref": [
      "r73",
      "r74",
      "r75",
      "r77",
      "r82",
      "r84",
      "r125",
      "r189",
      "r190",
      "r191",
      "r198",
      "r199",
      "r285",
      "r287"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cumulative amount of the reporting entity's undistributed earnings or deficit.",
        "label": "Retained Earnings [Member]",
        "terseLabel": "Accumulated Deficit"
       }
      }
     },
     "localname": "RetainedEarningsMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax": {
     "auth_ref": [
      "r100",
      "r101",
      "r103",
      "r108",
      "r109",
      "r113",
      "r114",
      "r115",
      "r148",
      "r149",
      "r253"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited": {
       "order": 10050.0,
       "parentTag": "us-gaap_OperatingIncomeLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.",
        "label": "Revenue From Contract With Customer Excluding Assessed Tax",
        "terseLabel": "Total revenue"
       }
      }
     },
     "localname": "RevenueFromContractWithCustomerExcludingAssessedTax",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RevenueFromContractWithCustomerPolicyTextBlock": {
     "auth_ref": [
      "r67",
      "r140",
      "r141",
      "r142",
      "r143",
      "r144",
      "r145",
      "r146",
      "r147",
      "r152"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for revenue from contract with customer.",
        "label": "Revenue From Contract With Customer Policy [Text Block]",
        "terseLabel": "Revenue Recognition"
       }
      }
     },
     "localname": "RevenueFromContractWithCustomerPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SaleOfStockNameOfTransactionDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sale of the entity's stock, including, but not limited to, initial public offering (IPO) and private placement.",
        "label": "Sale Of Stock Name Of Transaction [Domain]",
        "terseLabel": "Sale of Stock"
       }
      }
     },
     "localname": "SaleOfStockNameOfTransactionDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule for securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by Antidilutive Securities.",
        "label": "Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]",
        "terseLabel": "Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]"
       }
      }
     },
     "localname": "ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareScheduleOfDilutiveSharesExcludedFromCalculationOfDilutedNetLossPerShareDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock": {
     "auth_ref": [
      "r87"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by antidilutive securities.",
        "label": "Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block]",
        "terseLabel": "Schedule of Dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share"
       }
      }
     },
     "localname": "ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureNetLossPerShareTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock": {
     "auth_ref": [
      "r167",
      "r184",
      "r193"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.",
        "label": "Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block]",
        "terseLabel": "Summary of Recognized Stock-Based Compensation"
       }
      }
     },
     "localname": "ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock": {
     "auth_ref": [
      "r176"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the changes in outstanding nonvested restricted stock units.",
        "label": "Schedule Of Nonvested Restricted Stock Units Activity Table [Text Block]",
        "terseLabel": "Summary of Restricted Common Stock"
       }
      }
     },
     "localname": "ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable": {
     "auth_ref": [
      "r69",
      "r238",
      "r240"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of quantitative and qualitative information pertaining to related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.",
        "label": "Schedule Of Related Party Transactions By Related Party [Table]",
        "terseLabel": "Schedule Of Related Party Transactions By Related Party [Table]"
       }
      }
     },
     "localname": "ScheduleOfRelatedPartyTransactionsByRelatedPartyTable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfRestrictedCashAndCashEquivalentsTextBlock": {
     "auth_ref": [
      "r7",
      "r65",
      "r266",
      "r276"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of cash and cash equivalents restricted as to withdrawal or usage.",
        "label": "Schedule Of Restricted Cash And Cash Equivalents [Text Block]",
        "terseLabel": "Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash"
       }
      }
     },
     "localname": "ScheduleOfRestrictedCashAndCashEquivalentsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable": {
     "auth_ref": [
      "r168",
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about share-based payment arrangement.",
        "label": "Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]",
        "terseLabel": "Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]"
       }
      }
     },
     "localname": "ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock": {
     "auth_ref": [
      "r170",
      "r179",
      "r180"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.",
        "label": "Schedule Of Share Based Compensation Stock Options Activity Table [Text Block]",
        "terseLabel": "Summary of Options to Purchase Common Stock"
       }
      }
     },
     "localname": "ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ShareBasedCompensation": {
     "auth_ref": [
      "r57"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited": {
       "order": 10110.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of noncash expense for share-based payment arrangement.",
        "label": "Share Based Compensation",
        "terseLabel": "Stock-based compensation"
       }
      }
     },
     "localname": "ShareBasedCompensation",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate": {
     "auth_ref": [
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Discount rate from fair value on purchase date that participants pay for shares.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Discount From Market Price Purchase Date",
        "terseLabel": "Purchase price of common stock, percentage"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber": {
     "auth_ref": [
      "r177"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number",
        "periodEndLabel": "Number of Shares, Unvested, ending balance",
        "periodStartLabel": "Number of Shares, Unvested, beginning balance"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Roll Forward",
        "terseLabel": "Number of Shares"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r177"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value",
        "periodEndLabel": "Weighted Average Grant Date Fair Value per Share, Unvested, ending balance",
        "periodStartLabel": "Weighted Average Grant Date Fair Value per Share, Unvested, beginning balance"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value Roll Forward",
        "terseLabel": "Weighted-average grant-date fair value"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod": {
     "auth_ref": [
      "r178"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period",
        "negatedLabel": "Number of Shares, Vested"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r178"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value",
        "terseLabel": "Weighted Average Grant Date Fair Value per Share, Vested"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award [Line Items]",
        "terseLabel": "Share Based Compensation Arrangement By Share Based Payment Award [Line Items]"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRecognizedStockBasedCompensationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant": {
     "auth_ref": [
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant",
        "terseLabel": "Common stock, shares available for issuance"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber": {
     "auth_ref": [
      "r173"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number",
        "terseLabel": "Number of Options, Exercisable"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod": {
     "auth_ref": [
      "r175"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period",
        "negatedLabel": "Number of Options, Forfeited"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Gross number of share options (or share units) granted during the period.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross",
        "terseLabel": "Number of Options, Granted"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue": {
     "auth_ref": [
      "r187"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value",
        "terseLabel": "Aggregate Intrinsic Value, Outstanding"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber": {
     "auth_ref": [
      "r172",
      "r187"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of options outstanding, including both vested and non-vested options.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number",
        "periodEndLabel": "Number of Options, Outstanding, ending balance",
        "periodStartLabel": "Number of Options, Outstanding, beginning balance"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice": {
     "auth_ref": [
      "r171"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price",
        "periodEndLabel": "Weighted average exercise price, Outstanding, ending balance",
        "periodStartLabel": "Weighted average exercise price, Outstanding, beginning balance"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice": {
     "auth_ref": [
      "r182"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Exercise Price",
        "terseLabel": "Weighted average exercise price, Exercisable"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue": {
     "auth_ref": [
      "r180"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Aggregate Intrinsic Value",
        "terseLabel": "Aggregate Intrinsic Value, Vested or expected to vest"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber": {
     "auth_ref": [
      "r181"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number",
        "terseLabel": "Number of Options, Vested and expected to vest"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice": {
     "auth_ref": [
      "r181"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price",
        "terseLabel": "Weighted average exercise price, Vested and expected to vest"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain": {
     "auth_ref": [
      "r166",
      "r169"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Award under share-based payment arrangement.",
        "label": "Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain]",
        "terseLabel": "Award Type"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedCommonStockDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price at which option holders acquired shares when converting their stock options into shares.",
        "label": "Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price",
        "terseLabel": "Weighted average exercise price, Exercised"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.",
        "label": "Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price",
        "terseLabel": "Weighted average exercise price, Forfeited"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.",
        "label": "Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price",
        "terseLabel": "Weighted average exercise price, Granted"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1": {
     "auth_ref": [
      "r187"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.",
        "label": "Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1",
        "terseLabel": "Aggregate Intrinsic Value, Exercisable"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2": {
     "auth_ref": [
      "r181"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2",
        "terseLabel": "Weighted Average Remaining Contractual Term, Outstanding (in years)"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1": {
     "auth_ref": [
      "r182"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining contractual term for fully vested and expected to vest exercisable or convertible options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Exercisable Weighted Average Remaining Contractual Term1",
        "terseLabel": "Weighted Average Remaining Contractual Term, Exercisable (In years)"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1": {
     "auth_ref": [
      "r181"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.",
        "label": "Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1",
        "terseLabel": "Weighted Average Remaining Contractual Term, Vested and expected to vest (In years)"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_SharesIssuedPricePerShare": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Per share or per unit amount of equity securities issued.",
        "label": "Shares Issued Price Per Share",
        "terseLabel": "Share price"
       }
      }
     },
     "localname": "SharesIssuedPricePerShare",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_SignificantAccountingPoliciesTextBlock": {
     "auth_ref": [
      "r72"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for all significant accounting policies of the reporting entity.",
        "label": "Significant Accounting Policies [Text Block]",
        "terseLabel": "Summary of Significant Accounting Policies"
       }
      }
     },
     "localname": "SignificantAccountingPoliciesTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_StatementEquityComponentsAxis": {
     "auth_ref": [
      "r30",
      "r73",
      "r74",
      "r75",
      "r77",
      "r82",
      "r84",
      "r91",
      "r125",
      "r135",
      "r136",
      "r189",
      "r190",
      "r191",
      "r198",
      "r199",
      "r226",
      "r227",
      "r228",
      "r229",
      "r230",
      "r231",
      "r285",
      "r286",
      "r287"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by component of equity.",
        "label": "Statement Equity Components [Axis]",
        "terseLabel": "Accumulated Other Comprehensive Income"
       }
      }
     },
     "localname": "StatementEquityComponentsAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Statement [Line Items]",
        "terseLabel": "Statement [Line Items]"
       }
      }
     },
     "localname": "StatementLineItems",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfCashFlowsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement Of Cash Flows [Abstract]"
       }
      }
     },
     "localname": "StatementOfCashFlowsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfFinancialPositionAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement Of Financial Position [Abstract]"
       }
      }
     },
     "localname": "StatementOfFinancialPositionAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement Of Income And Comprehensive Income [Abstract]"
       }
      }
     },
     "localname": "StatementOfIncomeAndComprehensiveIncomeAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfStockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement Of Stockholders Equity [Abstract]"
       }
      }
     },
     "localname": "StatementOfStockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementTable": {
     "auth_ref": [
      "r73",
      "r74",
      "r75",
      "r91",
      "r253"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule reflecting a Statement of Income, Statement of Cash Flows, Statement of Financial Position, Statement of Shareholders' Equity and Other Comprehensive Income, or other statement as needed.",
        "label": "Statement [Table]",
        "terseLabel": "Statement [Table]"
       }
      }
     },
     "localname": "StatementTable",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StockIssuedDuringPeriodSharesNewIssues": {
     "auth_ref": [
      "r11",
      "r12",
      "r135",
      "r136"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of new stock issued during the period.",
        "label": "Stock Issued During Period Shares New Issues",
        "terseLabel": "Issuance of common stock upon follow-on public offering, net of issuance costs (in shares)",
        "verboseLabel": "Public offerings"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodSharesNewIssues",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised": {
     "auth_ref": [
      "r11",
      "r12",
      "r135",
      "r136",
      "r174"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of share options (or share units) exercised during the current period.",
        "label": "Stock Issued During Period Shares Stock Options Exercised",
        "negatedLabel": "Number of Options, Exercised",
        "terseLabel": "Exercise of stock options (in shares)"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodSharesStockOptionsExercised",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfOptionsToPurchaseCommonStockDetails",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_StockIssuedDuringPeriodValueNewIssues": {
     "auth_ref": [
      "r11",
      "r12",
      "r135",
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.",
        "label": "Stock Issued During Period Value New Issues",
        "terseLabel": "Issuance of common stock upon follow-on public offering, net of issuance costs"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodValueNewIssues",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised": {
     "auth_ref": [
      "r30",
      "r135",
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value of stock issued as a result of the exercise of stock options.",
        "label": "Stock Issued During Period Value Stock Options Exercised",
        "terseLabel": "Exercise of stock options"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodValueStockOptionsExercised",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockholdersEquity": {
     "auth_ref": [
      "r12",
      "r16",
      "r17",
      "r68",
      "r117",
      "r124",
      "r224"
     ],
     "calculation": {
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited": {
       "order": 10020.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.",
        "label": "Stockholders Equity",
        "periodEndLabel": "Ending balance",
        "periodStartLabel": "Beginning balance",
        "totalLabel": "Total stockholders' equity"
       }
      }
     },
     "localname": "StockholdersEquity",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited",
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementOfStockholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Stockholders Equity [Abstract]",
        "terseLabel": "Stockholders' equity:"
       }
      }
     },
     "localname": "StockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_SubsidiarySaleOfStockAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of sale of the entity's stock.",
        "label": "Subsidiary Sale Of Stock [Axis]",
        "terseLabel": "Sale of Stock"
       }
      }
     },
     "localname": "SubsidiarySaleOfStockAxis",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails",
      "http://www.alector.com/20210331/taxonomy/role/DisclosureTheCompanyAndLiquidityAdditionalInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_TypeOfRevenueExtensibleList": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicates type of revenue from product and service. Includes, but is not limited to, revenue from contract with customer and other sources.",
        "label": "Type Of Revenue Extensible List",
        "terseLabel": "Type of Revenue [Extensible List]"
       }
      }
     },
     "localname": "TypeOfRevenueExtensibleList",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "extensibleListItemType"
    },
    "us-gaap_USTreasurySecuritiesMember": {
     "auth_ref": [
      "r154",
      "r162",
      "r272"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This category includes information about debt securities issued by the United States Department of the Treasury and backed by the United States government. Such securities primarily consist of treasury bills (short-term maturities - one year or less), treasury notes (intermediate term maturities - two to ten years), and treasury bonds (long-term maturities - ten to thirty years).",
        "label": "U S Treasury Securities [Member]",
        "terseLabel": "U.S Government Treasury Securities"
       }
      }
     },
     "localname": "USTreasurySecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_UnrealizedGainLossOnInvestments": {
     "auth_ref": [
      "r58"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unrealized gain (loss) on investment.",
        "label": "Unrealized Gain Loss On Investments",
        "terseLabel": "Unrealized gains or loss on money market funds"
       }
      }
     },
     "localname": "UnrealizedGainLossOnInvestments",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UseOfEstimates": {
     "auth_ref": [
      "r92",
      "r93",
      "r95",
      "r96",
      "r97",
      "r98",
      "r99"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for the use of estimates in the preparation of financial statements in conformity with generally accepted accounting principles.",
        "label": "Use Of Estimates",
        "terseLabel": "Use of Estimates"
       }
      }
     },
     "localname": "UseOfEstimates",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_WeightedAverageNumberOfShareOutstandingBasicAndDiluted": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).",
        "label": "Weighted Average Number Of Share Outstanding Basic And Diluted",
        "terseLabel": "Shares used in computing net loss per share, basic and diluted"
       }
      }
     },
     "localname": "WeightedAverageNumberOfShareOutstandingBasicAndDiluted",
     "nsuri": "http://fasb.org/us-gaap/2020-01-31",
     "presentation": [
      "http://www.alector.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited"
     ],
     "xbrltype": "sharesItemType"
    }
   },
   "unitCount": 4
  }
 },
 "std_ref": {
  "r0": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "205",
   "URI": "http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760"
  },
  "r1": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "205",
   "URI": "http://asc.fasb.org/topic&trid=2122149"
  },
  "r10": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(17))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r100": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599"
  },
  "r101": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599"
  },
  "r102": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599"
  },
  "r103": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599"
  },
  "r104": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599"
  },
  "r105": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599"
  },
  "r106": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599"
  },
  "r107": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "31",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599"
  },
  "r108": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599"
  },
  "r109": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599"
  },
  "r11": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(28))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r110": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599"
  },
  "r111": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599"
  },
  "r112": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599"
  },
  "r113": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "40",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599"
  },
  "r114": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "41",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599"
  },
  "r115": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "42",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599"
  },
  "r116": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=121593590&loc=d3e4647-111522"
  },
  "r117": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 4.E)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707"
  },
  "r118": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121553693&loc=d3e26853-111562"
  },
  "r119": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563"
  },
  "r12": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(29))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r120": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563"
  },
  "r121": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563"
  },
  "r122": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563"
  },
  "r123": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=121645371&loc=d3e27198-111563"
  },
  "r124": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571"
  },
  "r125": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437"
  },
  "r126": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454"
  },
  "r127": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r128": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r129": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230"
  },
  "r13": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(1))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r130": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "440",
   "URI": "http://asc.fasb.org/extlink&oid=121559207&loc=d3e25336-109308"
  },
  "r131": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "440",
   "URI": "http://asc.fasb.org/extlink&oid=121559207&loc=d3e25336-109308"
  },
  "r132": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "440",
   "URI": "http://asc.fasb.org/topic&trid=2144648"
  },
  "r133": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355"
  },
  "r134": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "450",
   "URI": "http://asc.fasb.org/topic&trid=2127136"
  },
  "r135": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644"
  },
  "r136": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.3-04)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770"
  },
  "r137": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044"
  },
  "r138": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044"
  },
  "r139": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130551-203045"
  },
  "r14": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(3))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r140": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130561-203045"
  },
  "r141": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130563-203045"
  },
  "r142": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130563-203045"
  },
  "r143": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "19",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130564-203045"
  },
  "r144": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045"
  },
  "r145": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045"
  },
  "r146": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045"
  },
  "r147": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130566-203045"
  },
  "r148": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045"
  },
  "r149": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045"
  },
  "r15": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(4))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r150": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045"
  },
  "r151": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045"
  },
  "r152": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "606",
   "URI": "http://asc.fasb.org/topic&trid=49130388"
  },
  "r153": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(i)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r154": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(ii)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r155": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(01)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r156": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r157": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(A)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r158": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(B)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r159": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(C)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r16": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r160": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(03)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r161": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(n)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920"
  },
  "r162": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921"
  },
  "r163": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(d)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947"
  },
  "r164": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "80",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948"
  },
  "r165": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "35",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121326096&loc=d3e4534-113899"
  },
  "r166": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r167": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r168": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r169": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a),(g)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r17": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(31))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r170": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r171": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r172": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(i)-(ii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r173": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r174": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r175": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(3)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r176": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r177": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(i)-(ii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r178": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(iii)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r179": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r18": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(32))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r180": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r181": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r182": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r183": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(g)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r184": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r185": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)(1)(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r186": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r187": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r188": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=SL79508275-113901"
  },
  "r189": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r19": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(7))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r190": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(f)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r191": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r192": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(g)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r193": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 14.F)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809"
  },
  "r194": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120383193&loc=d3e11149-113907"
  },
  "r195": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120383193&loc=d3e11178-113907"
  },
  "r196": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "718",
   "URI": "http://asc.fasb.org/topic&trid=2228938"
  },
  "r197": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "730",
   "URI": "http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373"
  },
  "r198": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)(2)",
   "Topic": "740"
  },
  "r199": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)(3)",
   "Topic": "740"
  },
  "r2": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765"
  },
  "r20": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(8))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r200": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "19",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683"
  },
  "r201": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=108774443&loc=SL4569643-111683"
  },
  "r202": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988"
  },
  "r203": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988"
  },
  "r204": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r205": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r206": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(3)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r207": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c),(3)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r208": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bb)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685"
  },
  "r209": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685"
  },
  "r21": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.1)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r210": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4J",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=120409616&loc=SL4591551-111686"
  },
  "r211": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4K",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=120409616&loc=SL4591552-111686"
  },
  "r212": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "810",
   "URI": "http://asc.fasb.org/topic&trid=2197479"
  },
  "r213": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r214": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r215": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bb)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r216": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bbb)(1)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r217": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bbb)(2)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r218": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r219": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258"
  },
  "r22": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.17)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r220": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=d3e19279-110258"
  },
  "r221": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258"
  },
  "r222": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "60",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=7493716&loc=d3e21868-110260"
  },
  "r223": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=121572278&loc=d3e13279-108611"
  },
  "r224": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612"
  },
  "r225": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "230",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=98513438&loc=d3e33268-110906"
  },
  "r226": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900"
  },
  "r227": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r228": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(b)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r229": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(c)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r23": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19(a))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r230": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(d)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r231": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901"
  },
  "r232": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977"
  },
  "r233": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977"
  },
  "r234": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r235": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r236": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r237": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r238": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r239": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39599-107864"
  },
  "r24": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19-26)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r240": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864"
  },
  "r241": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864"
  },
  "r242": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "850",
   "URI": "http://asc.fasb.org/topic&trid=2122745"
  },
  "r243": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r244": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r245": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r246": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r247": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r248": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r249": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r25": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.2)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r250": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r251": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r252": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "910",
   "URI": "http://asc.fasb.org/extlink&oid=119991564&loc=SL119991595-234733"
  },
  "r253": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 11.L)",
   "Topic": "924",
   "URI": "http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856"
  },
  "r254": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(a)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e61929-109447"
  },
  "r255": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(b)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e61929-109447"
  },
  "r256": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(a)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62059-109447"
  },
  "r257": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(b)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62059-109447"
  },
  "r258": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(a)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62395-109447"
  },
  "r259": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(b)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62395-109447"
  },
  "r26": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.20)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r260": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "33",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(a)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447"
  },
  "r261": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "33",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(b)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e62479-109447"
  },
  "r262": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "35A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(a)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447"
  },
  "r263": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "35A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(b)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447"
  },
  "r264": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(c)(1)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e61872-109447"
  },
  "r265": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "235",
   "Subparagraph": "(c)(2)",
   "Topic": "932",
   "URI": "http://asc.fasb.org/extlink&oid=68064819&loc=d3e61872-109447"
  },
  "r266": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(1)(a))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r267": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(11))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r268": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(23))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r269": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(22))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r27": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.21)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r270": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(26))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r271": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "235",
   "Subparagraph": "(SX 210.9-05(b)(2))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884"
  },
  "r272": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "320",
   "Subparagraph": "(b)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120252992&loc=d3e62557-112803"
  },
  "r273": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "320",
   "Subparagraph": "(a)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120252992&loc=SL120269850-112803"
  },
  "r274": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "825",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=108315417&loc=d3e61044-112788"
  },
  "r275": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(12))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r276": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(2))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r277": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(23)(a)(3))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r278": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(23)(a)(4))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r279": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(25))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r28": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.24)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r280": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(8))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r281": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(18))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r282": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(22))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r283": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Subparagraph": "(d)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121643868&loc=SL117782755-158439"
  },
  "r284": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "29F",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "40",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121639165&loc=SL117819544-158441"
  },
  "r285": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(e)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r286": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(f)(1)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r287": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(f)(2)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r288": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(i)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r289": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(ii)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r29": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.29)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r290": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(h)(2)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641"
  },
  "r291": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "210",
   "Topic": "954",
   "URI": "http://asc.fasb.org/extlink&oid=120413173&loc=SL116631458-115580"
  },
  "r292": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "985",
   "URI": "http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756"
  },
  "r293": {
   "Name": "Exchange Act",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "b"
  },
  "r294": {
   "Name": "Exchange Act",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "d1-1"
  },
  "r295": {
   "Name": "Form 10-Q",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "308",
   "Subsection": "a"
  },
  "r296": {
   "Name": "Forms 10-K, 10-Q, 20-F",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "13",
   "Subsection": "a-1"
  },
  "r297": {
   "Name": "Regulation 12B",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "b-2"
  },
  "r298": {
   "Name": "Regulation S-T",
   "Number": "232",
   "Publisher": "SEC",
   "Section": "405"
  },
  "r3": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765"
  },
  "r30": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.29-31)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r31": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.9)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r32": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226024-175313"
  },
  "r33": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580"
  },
  "r34": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580"
  },
  "r35": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580"
  },
  "r36": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580"
  },
  "r37": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=d3e681-108580"
  },
  "r38": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580"
  },
  "r39": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL34724394-108580"
  },
  "r4": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765"
  },
  "r40": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580"
  },
  "r41": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580"
  },
  "r42": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580"
  },
  "r43": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580"
  },
  "r44": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580"
  },
  "r45": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=121641772&loc=d3e557-108580"
  },
  "r46": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(20))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227"
  },
  "r47": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(24))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227"
  },
  "r48": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(4))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227"
  },
  "r49": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03.4)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227"
  },
  "r5": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=121566466&loc=d3e6801-107765"
  },
  "r50": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03.9)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227"
  },
  "r51": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585"
  },
  "r52": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585"
  },
  "r53": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3000-108585"
  },
  "r54": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "24",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3521-108585"
  },
  "r55": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585"
  },
  "r56": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585"
  },
  "r57": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585"
  },
  "r58": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585"
  },
  "r59": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585"
  },
  "r6": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=121566466&loc=d3e6812-107765"
  },
  "r60": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121586364&loc=d3e3044-108585"
  },
  "r61": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121583591&loc=d3e4273-108586"
  },
  "r62": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586"
  },
  "r63": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586"
  },
  "r64": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586"
  },
  "r65": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=121583591&loc=SL98516268-108586"
  },
  "r66": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790"
  },
  "r67": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=84158767&loc=d3e18823-107790"
  },
  "r68": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(g)(1)(ii))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r69": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(k))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r7": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(1))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r70": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(m)(1)(iii))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r71": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08.(k)(1))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r72": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "235",
   "URI": "http://asc.fasb.org/topic&trid=2122369"
  },
  "r73": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "23",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=115929471&loc=d3e21914-107793"
  },
  "r74": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "24",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=115929471&loc=d3e21930-107793"
  },
  "r75": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=115929471&loc=d3e21711-107793"
  },
  "r76": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(2)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794"
  },
  "r77": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(3)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794"
  },
  "r78": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794"
  },
  "r79": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794"
  },
  "r8": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(13))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r80": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794"
  },
  "r81": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22595-107794"
  },
  "r82": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22644-107794"
  },
  "r83": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22658-107794"
  },
  "r84": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794"
  },
  "r85": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "60B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=121326447&loc=SL5780133-109256"
  },
  "r86": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=121326447&loc=d3e1337-109256"
  },
  "r87": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257"
  },
  "r88": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=6371337&loc=d3e3630-109257"
  },
  "r89": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=109243012&loc=SL65017193-207537"
  },
  "r9": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(14))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r90": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "260",
   "URI": "http://asc.fasb.org/topic&trid=2144383"
  },
  "r91": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "272",
   "URI": "http://asc.fasb.org/extlink&oid=6828210&loc=d3e70191-108054"
  },
  "r92": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e5967-108592"
  },
  "r93": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e5967-108592"
  },
  "r94": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e5967-108592"
  },
  "r95": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6161-108592"
  },
  "r96": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6191-108592"
  },
  "r97": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6061-108592"
  },
  "r98": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6132-108592"
  },
  "r99": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6143-108592"
  }
 },
 "version": "2.1"
}
