| IRS990/AccountantCompileOrReviewInd | 0 | 0 |
| IRS990/ActivitiesConductedPrtshpInd | 0 | 0 |
| IRS990/ActivityOrMissionDesc | 0 | SEE SCHEDULE O ATTACHEDTHE MILL VALLEY LIBRARY FOUNDATION RAISES FUNDS TO SUPPLEMENT THE FUNDING PROVIDED BY THE CITY OF MILL VALLEY TO THE MILL VALLEY PUBLIC LIBRARY WITH THE OBJECTIVE TO INSURE THAT THE LIBRARY WILL BE ABLE TO PROVIDE HIGH QUALITY PROGRAMS AND SERVICES IN PERPETUITY. |
| IRS990/AdvertisingGrp/FundraisingAmt | 0 | 3021 |
| IRS990/AdvertisingGrp/ManagementAndGeneralAmt | 0 | 1812 |
| IRS990/AdvertisingGrp/TotalAmt | 0 | 4833 |
| IRS990/AllOtherContributionsAmt | 0 | 162729 |
| IRS990/BooksInCareOfDetail/BusinessName/BusinessNameLine1Txt | 0 | THE ORGANIZATION |
| IRS990/BooksInCareOfDetail/PhoneNum | 0 | 4159872760 |
| IRS990/BooksInCareOfDetail/USAddress/AddressLine1Txt | 0 | 375 THROCKMORTON AVE |
| IRS990/BooksInCareOfDetail/USAddress/CityNm | 0 | MILL VALLEY |
| IRS990/BooksInCareOfDetail/USAddress/StateAbbreviationCd | 0 | CA |
| IRS990/BooksInCareOfDetail/USAddress/ZIPCd | 0 | 94941 |
| IRS990/BusinessRlnWith35CtrlEntInd | 0 | 0 |
| IRS990/BusinessRlnWithFamMemInd | 0 | 0 |
| IRS990/BusinessRlnWithOrgMemInd | 0 | 0 |
| IRS990/CashNonInterestBearingGrp/BOYAmt | 0 | 103986 |
| IRS990/CashNonInterestBearingGrp/EOYAmt | 0 | 62235 |
| IRS990/ChangeToOrgDocumentsInd | 0 | 0 |
| IRS990/CntrctRcvdGreaterThan100KCnt | 0 | 0 |
| IRS990/CollectionsOfArtInd | 0 | 0 |
| IRS990/CompensationFromOtherSrcsInd | 0 | 0 |
| IRS990/CompensationProcessCEOInd | 0 | 0 |
| IRS990/CompensationProcessOtherInd | 0 | 0 |
| IRS990/ConflictOfInterestPolicyInd | 0 | 0 |
| IRS990/ConservationEasementsInd | 0 | 0 |
| IRS990/ConsolidatedAuditFinclStmtInd | 0 | 0 |
| IRS990/CreditCounselingInd | 0 | 0 |
| IRS990/CYBenefitsPaidToMembersAmt | 0 | 0 |
| IRS990/CYContributionsGrantsAmt | 0 | 162729 |
| IRS990/CYGrantsAndSimilarPaidAmt | 0 | 132000 |
| IRS990/CYInvestmentIncomeAmt | 0 | 256808 |
| IRS990/CYOtherExpensesAmt | 0 | 92330 |
| IRS990/CYOtherRevenueAmt | 0 | 0 |
| IRS990/CYProgramServiceRevenueAmt | 0 | 0 |
| IRS990/CYRevenuesLessExpensesAmt | 0 | 195207 |
| IRS990/CYSalariesCompEmpBnftPaidAmt | 0 | 0 |
| IRS990/CYTotalExpensesAmt | 0 | 224330 |
| IRS990/CYTotalFundraisingExpenseAmt | 0 | 20654 |
| IRS990/CYTotalProfFndrsngExpnsAmt | 0 | 0 |
| IRS990/CYTotalRevenueAmt | 0 | 419537 |
| IRS990/DecisionsSubjectToApprovaInd | 0 | 0 |
| IRS990/DeductibleArtContributionInd | 0 | 0 |
| IRS990/DeductibleNonCashContriInd | 0 | 0 |
| IRS990/DelegationOfMgmtDutiesInd | 0 | 0 |
| IRS990/Desc | 0 | THE MILL VALLEY LIBRARY FOUNDATION DOES NOT PROVIDE ANY PROGRAM SERVICES. IT IS SOLELY A FUND RAISING ORGANIZATION. THE FOUNDATION PROGRAM CONSISTS OF DELIVERING FUNDS IN THE FORM OF GRANTS TO THE MILL VALLEY PUBLIC LIBRARY, TO PROVIDE FUNDING FOR SPECIFIC PROGRAMS DESIGNATED BY THE HEAD LIBRARIAN. |
| IRS990/DescribedInSection501c3Ind | 0 | 1 |
| IRS990/DisregardedEntityInd | 0 | 0 |
| IRS990/DocumentRetentionPolicyInd | 0 | 0 |
| IRS990/DonorAdvisedFundInd | 0 | 0 |
| IRS990/DonorRestrictionNetAssetsGrp/BOYAmt | 0 | 350000 |
| IRS990/DonorRestrictionNetAssetsGrp/EOYAmt | 0 | 350000 |
| IRS990/DonorRstrOrQuasiEndowmentsInd | 0 | 1 |
| IRS990/ElectionOfBoardMembersInd | 0 | 0 |
| IRS990/EmployeeCnt | 0 | 0 |
| IRS990/EngagedInExcessBenefitTransInd | 0 | 0 |
| IRS990/ExpenseAmt | 0 | 132000 |
| IRS990/FamilyOrBusinessRlnInd | 0 | 0 |
| IRS990/FederalGrantAuditRequiredInd | 0 | 0 |
| IRS990/FeesForServicesAccountingGrp/ManagementAndGeneralAmt | 0 | 16339 |
| IRS990/FeesForServicesAccountingGrp/TotalAmt | 0 | 16339 |
| IRS990/FeesForServicesOtherGrp/FundraisingAmt | 0 | 1061 |
| IRS990/FeesForServicesOtherGrp/ManagementAndGeneralAmt | 0 | 36548 |
| IRS990/FeesForServicesOtherGrp/TotalAmt | 0 | 37609 |
| IRS990/ForeignActivitiesInd | 0 | 0 |
| IRS990/ForeignFinancialAccountInd | 0 | 0 |
| IRS990/ForeignOfficeInd | 0 | 0 |
| IRS990/Form8282PropertyDisposedOfInd | 0 | 0 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 0 | 5.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 1 | 3.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 2 | 5.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 3 | 3.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 4 | 3.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 5 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 6 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 7 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 8 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 9 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 10 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 11 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 12 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 13 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 14 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 0 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 1 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 2 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 3 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 4 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 5 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 6 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 7 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 8 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 9 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 10 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 11 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 12 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 13 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 14 | X |
| IRS990/Form990PartVIISectionAGrp/OfficerInd | 0 | X |
| IRS990/Form990PartVIISectionAGrp/OfficerInd | 1 | X |
| IRS990/Form990PartVIISectionAGrp/OfficerInd | 2 | X |
| IRS990/Form990PartVIISectionAGrp/OfficerInd | 3 | X |
| IRS990/Form990PartVIISectionAGrp/OfficerInd | 4 | X |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 0 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 1 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 2 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 3 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 4 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 5 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 6 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 7 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 8 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 9 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 10 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 11 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 12 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 13 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 14 | 0 |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 0 | DEBORAH SORONDO |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 1 | STEPHEN DONAHUE |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 2 | JEFFREY HAMRICK |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 3 | DEBORAH MILLER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 4 | MICHELLE BUCKLES |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 5 | ABHI VALLABHANEMI |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 6 | STEPHEN LANG |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 7 | TOM DICKER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 8 | KATHRYN CICOLETTI |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 9 | ERIC ISSADORE |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 10 | TRACY PELL |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 11 | CAROL ZIMMERMAN |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 12 | KATE AZIMA |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 13 | SEAN WASSERMAN |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 14 | LYNN VEAR |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 0 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 1 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 2 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 3 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 4 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 5 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 6 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 7 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 8 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 9 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 10 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 11 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 12 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 13 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 14 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 0 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 1 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 2 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 3 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 4 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 5 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 6 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 7 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 8 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 9 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 10 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 11 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 12 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 13 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 14 | 0 |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 0 | PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 1 | SECRETARY |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 2 | TREASURER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 3 | CO-VICE PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 4 | CO-VICE PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 5 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 6 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 7 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 8 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 9 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 10 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 11 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 12 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 13 | BOARD MEMBER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 14 | BOARD MEMBER |
| IRS990/Form990ProvidedToGvrnBodyInd | 0 | 1 |
| IRS990/FormationYr | 0 | 1986 |
| IRS990/FormerOfcrEmployeesListedInd | 0 | 0 |
| IRS990/FSAuditedInd | 0 | 0 |
| IRS990/FundraisingActivitiesInd | 0 | 0 |
| IRS990/GainOrLossGrp/SecuritiesAmt | 0 | 90432 |
| IRS990/GamingActivitiesInd | 0 | 0 |
| IRS990/GoverningBodyVotingMembersCnt | 0 | 15 |
| IRS990/GrantAmt | 0 | 132000 |
| IRS990/GrantsToDomesticOrgsGrp/ProgramServicesAmt | 0 | 132000 |
| IRS990/GrantsToDomesticOrgsGrp/TotalAmt | 0 | 132000 |
| IRS990/GrantsToIndividualsInd | 0 | 0 |
| IRS990/GrantsToOrganizationsInd | 0 | 1 |
| IRS990/GrantToRelatedPersonInd | 0 | 0 |
| IRS990/GrossAmountSalesAssetsGrp/SecuritiesAmt | 0 | 90432 |
| IRS990/GrossReceiptsAmt | 0 | 419537 |
| IRS990/GroupReturnForAffiliatesInd | 0 | 0 |
| IRS990/IncludeFIN48FootnoteInd | 0 | 0 |
| IRS990/IndependentAuditFinclStmtInd | 0 | 0 |
| IRS990/IndependentVotingMemberCnt | 0 | 15 |
| IRS990/IndivRcvdGreaterThan100KCnt | 0 | 0 |
| IRS990/IndoorTanningServicesInd | 0 | 0 |
| IRS990/InfoInScheduleOPartIIIInd | 0 | X |
| IRS990/InfoInScheduleOPartIXInd | 0 | X |
| IRS990/InfoInScheduleOPartVIInd | 0 | X |
| IRS990/InformationTechnologyGrp/ManagementAndGeneralAmt | 0 | 3467 |
| IRS990/InformationTechnologyGrp/TotalAmt | 0 | 3467 |
| IRS990/InsuranceGrp/ManagementAndGeneralAmt | 0 | 4737 |
| IRS990/InsuranceGrp/TotalAmt | 0 | 4737 |
| IRS990/InvestmentIncomeGrp/ExclusionAmt | 0 | 166376 |
| IRS990/InvestmentIncomeGrp/TotalRevenueColumnAmt | 0 | 166376 |
| IRS990/InvestmentInJointVentureInd | 0 | 0 |
| IRS990/InvestmentsPubTradedSecGrp/BOYAmt | 0 | 5064322 |
| IRS990/InvestmentsPubTradedSecGrp/EOYAmt | 0 | 5997853 |
| IRS990/IRPDocumentCnt | 0 | 0 |
| IRS990/IRPDocumentW2GCnt | 0 | 0 |
| IRS990/LegalDomicileStateCd | 0 | CA |
| IRS990/LessCostOthBasisSalesExpnssGrp/SecuritiesAmt | 0 | 0 |
| IRS990/LoanOutstandingInd | 0 | 0 |
| IRS990/LobbyingActivitiesInd | 0 | 0 |
| IRS990/LocalChaptersInd | 0 | 0 |
| IRS990/MaterialDiversionOrMisuseInd | 0 | 0 |
| IRS990/MembersOrStockholdersInd | 0 | 0 |
| IRS990/MethodOfAccountingAccrualInd | 0 | X |
| IRS990/MinutesOfCommitteesInd | 0 | 1 |
| IRS990/MinutesOfGoverningBodyInd | 0 | 1 |
| IRS990/MissionDesc | 0 | SEE SCHEDULE O ATTACHEDTHE MILL VALLEY LIBRARY FOUNDATION RAISES FUNDS TO SUPPLEMENT THE FUNDING PROVIDED BY THE CITY OF MILL VALLEY TO THE MILL VALLEY PUBLIC LIBRARY WITH THE OBJECTIVE TO INSURE THAT THE LIBRARY WILL BE ABLE TO PROVIDE HIGH QUALITY PROGRAMS AND SERVICES IN PERPETUITY. |
| IRS990/MoreThan5000KToIndividualsInd | 0 | 0 |
| IRS990/MoreThan5000KToOrgInd | 0 | 0 |
| IRS990/NetAssetsOrFundBalancesBOYAmt | 0 | 5168308 |
| IRS990/NetAssetsOrFundBalancesEOYAmt | 0 | 6060088 |
| IRS990/NetGainOrLossInvestmentsGrp/RelatedOrExemptFuncIncomeAmt | 0 | 90432 |
| IRS990/NetGainOrLossInvestmentsGrp/TotalRevenueColumnAmt | 0 | 90432 |
| IRS990/NetUnrelatedBusTxblIncmAmt | 0 | 0 |
| IRS990/NetUnrlzdGainsLossesInvstAmt | 0 | 696573 |
| IRS990/NoDonorRestrictionNetAssetsGrp/BOYAmt | 0 | 4818308 |
| IRS990/NoDonorRestrictionNetAssetsGrp/EOYAmt | 0 | 5710088 |
| IRS990/NoListedPersonsCompensatedInd | 0 | X |
| IRS990/NondeductibleContributionsInd | 0 | 0 |
| IRS990/OfficeExpensesGrp/FundraisingAmt | 0 | 16572 |
| IRS990/OfficeExpensesGrp/ManagementAndGeneralAmt | 0 | 1543 |
| IRS990/OfficeExpensesGrp/TotalAmt | 0 | 18115 |
| IRS990/OfficerMailingAddressInd | 0 | 0 |
| IRS990/OperateHospitalInd | 0 | 0 |
| IRS990/Organization501c3Ind | 0 | X |
| IRS990/OrganizationFollowsFASB117Ind | 0 | X |
| IRS990/OtherChangesInNetAssetsAmt | 0 | 0 |
| IRS990/OtherExpensesGrp/Desc | 0 | OTHER |
| IRS990/OtherExpensesGrp/Desc | 1 | LEGACY PROGRAM |
| IRS990/OtherExpensesGrp/ManagementAndGeneralAmt | 0 | 4759 |
| IRS990/OtherExpensesGrp/ManagementAndGeneralAmt | 1 | 2471 |
| IRS990/OtherExpensesGrp/TotalAmt | 0 | 4759 |
| IRS990/OtherExpensesGrp/TotalAmt | 1 | 2471 |
| IRS990/OwnWebsiteInd | 0 | X |
| IRS990/PartialLiquidationInd | 0 | 0 |
| IRS990/PoliticalCampaignActyInd | 0 | 0 |
| IRS990/PrincipalOfficerNm | 0 | DEBORAH SORONDO |
| IRS990/ProfessionalFundraisingInd | 0 | 0 |
| IRS990/ProhibitedTaxShelterTransInd | 0 | 0 |
| IRS990/PYBenefitsPaidToMembersAmt | 0 | 0 |
| IRS990/PYContributionsGrantsAmt | 0 | 2490676 |
| IRS990/PYExcessBenefitTransInd | 0 | 0 |
| IRS990/PYGrantsAndSimilarPaidAmt | 0 | 100100 |
| IRS990/PYInvestmentIncomeAmt | 0 | 94628 |
| IRS990/PYOtherExpensesAmt | 0 | 67131 |
| IRS990/PYOtherRevenueAmt | 0 | 0 |
| IRS990/PYProgramServiceRevenueAmt | 0 | 0 |
| IRS990/PYRevenuesLessExpensesAmt | 0 | 2418073 |
| IRS990/PYSalariesCompEmpBnftPaidAmt | 0 | 0 |
| IRS990/PYTotalExpensesAmt | 0 | 167231 |
| IRS990/PYTotalProfFndrsngExpnsAmt | 0 | 0 |
| IRS990/PYTotalRevenueAmt | 0 | 2585304 |
| IRS990/QuidProQuoContributionsInd | 0 | 0 |
| IRS990/ReconcilationRevenueExpnssAmt | 0 | 195207 |
| IRS990/RelatedEntityInd | 0 | 1 |
| IRS990/RelatedOrganizationCtrlEntInd | 0 | 0 |
| IRS990/ReportInvestmentsOtherSecInd | 0 | 0 |
| IRS990/ReportLandBuildingEquipmentInd | 0 | 0 |
| IRS990/ReportOtherAssetsInd | 0 | 0 |
| IRS990/ReportOtherLiabilitiesInd | 0 | 0 |
| IRS990/ReportProgramRelatedInvstInd | 0 | 0 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/CurrentTaxYearAmt | 0 | 162729 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/CurrentTaxYearMinus1YearAmt | 0 | 2490676 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/CurrentTaxYearMinus2YearsAmt | 0 | 170845 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/CurrentTaxYearMinus3YearsAmt | 0 | 150440 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/CurrentTaxYearMinus4YearsAmt | 0 | 129022 |
| IRS990ScheduleA/GiftsGrantsContriRcvd170Grp/TotalAmt | 0 | 3103712 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/CurrentTaxYearAmt | 0 | 256808 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/CurrentTaxYearMinus1YearAmt | 0 | 295407 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/CurrentTaxYearMinus2YearsAmt | 0 | -418486 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/CurrentTaxYearMinus3YearsAmt | 0 | 322181 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/CurrentTaxYearMinus4YearsAmt | 0 | 68487 |
| IRS990ScheduleA/GrossInvestmentIncome170Grp/TotalAmt | 0 | 524397 |
| IRS990ScheduleA/OtherIncome170Grp/CurrentTaxYearMinus3YearsAmt | 0 | 717 |
| IRS990ScheduleA/OtherIncome170Grp/TotalAmt | 0 | 717 |
| IRS990ScheduleA/PublicOrganization170Ind | 0 | X |
| IRS990ScheduleA/PublicSupportCY170Pct | 0 | 0.85530 |
| IRS990ScheduleA/PublicSupportPY170Pct | 0 | 0.89100 |
| IRS990ScheduleA/PublicSupportTotal170Amt | 0 | 3103712 |
| IRS990ScheduleA/ThirtyThrPctSuprtTestsCY170Ind | 0 | X |
| IRS990ScheduleA/TotalCalendarYear170Grp/CurrentTaxYearAmt | 0 | 162729 |
| IRS990ScheduleA/TotalCalendarYear170Grp/CurrentTaxYearMinus1YearAmt | 0 | 2490676 |
| IRS990ScheduleA/TotalCalendarYear170Grp/CurrentTaxYearMinus2YearsAmt | 0 | 170845 |
| IRS990ScheduleA/TotalCalendarYear170Grp/CurrentTaxYearMinus3YearsAmt | 0 | 150440 |
| IRS990ScheduleA/TotalCalendarYear170Grp/CurrentTaxYearMinus4YearsAmt | 0 | 129022 |
| IRS990ScheduleA/TotalCalendarYear170Grp/TotalAmt | 0 | 3103712 |
| IRS990ScheduleA/TotalSupportAmt | 0 | 3628826 |
| IRS990ScheduleB/ContributorInformationGrp/ContributorBusinessName/BusinessNameLine1 | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorNum | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorUSAddress/AddressLine1 | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorUSAddress/AddressLine2 | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorUSAddress/City | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorUSAddress/State | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/ContributorUSAddress/ZIPCode | 0 | RESTRICTED |
| IRS990ScheduleB/ContributorInformationGrp/TotalContributionsAmt | 0 | RESTRICTED |
| IRS990/ScheduleBRequiredInd | 0 | 1 |
| IRS990ScheduleD/AgentTrusteeEtcInd | 0 | 0 |
| IRS990ScheduleD/CYEndwmtFundGrp/BeginningYearBalanceAmt | 0 | 5064322 |
| IRS990ScheduleD/CYEndwmtFundGrp/ContributionsAmt | 0 | 162729 |
| IRS990ScheduleD/CYEndwmtFundGrp/EndYearBalanceAmt | 0 | 5259529 |
| IRS990ScheduleD/CYEndwmtFundGrp/GrantsOrScholarshipsAmt | 0 | 132000 |
| IRS990ScheduleD/CYEndwmtFundGrp/InvestmentEarningsOrLossesAmt | 0 | 256808 |
| IRS990ScheduleD/CYEndwmtFundGrp/OtherExpendituresAmt | 0 | 92330 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/BeginningYearBalanceAmt | 0 | 2490334 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/ContributionsAmt | 0 | 2490676 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/EndYearBalanceAmt | 0 | 5064322 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/GrantsOrScholarshipsAmt | 0 | 100100 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/InvestmentEarningsOrLossesAmt | 0 | 295407 |
| IRS990ScheduleD/CYMinus1YrEndwmtFundGrp/OtherExpendituresAmt | 0 | 111995 |
| IRS990ScheduleD/CYMinus2YrEndwmtFundGrp/BeginningYearBalanceAmt | 0 | 2900681 |
| IRS990ScheduleD/CYMinus2YrEndwmtFundGrp/ContributionsAmt | 0 | 6500 |
| IRS990ScheduleD/CYMinus2YrEndwmtFundGrp/EndYearBalanceAmt | 0 | 2490334 |
| IRS990ScheduleD/CYMinus2YrEndwmtFundGrp/GrantsOrScholarshipsAmt | 0 | 6500 |
| IRS990ScheduleD/CYMinus2YrEndwmtFundGrp/InvestmentEarningsOrLossesAmt | 0 | -410347 |
| IRS990ScheduleD/CYMinus3YrEndwmtFundGrp/BeginningYearBalanceAmt | 0 | 2559687 |
| IRS990ScheduleD/CYMinus3YrEndwmtFundGrp/ContributionsAmt | 0 | 106314 |
| IRS990ScheduleD/CYMinus3YrEndwmtFundGrp/EndYearBalanceAmt | 0 | 2900681 |
| IRS990ScheduleD/CYMinus3YrEndwmtFundGrp/GrantsOrScholarshipsAmt | 0 | 87500 |
| IRS990ScheduleD/CYMinus3YrEndwmtFundGrp/InvestmentEarningsOrLossesAmt | 0 | 322180 |
| IRS990ScheduleD/CYMinus4YrEndwmtFundGrp/BeginningYearBalanceAmt | 0 | 2541132 |
| IRS990ScheduleD/CYMinus4YrEndwmtFundGrp/ContributionsAmt | 0 | 64563 |
| IRS990ScheduleD/CYMinus4YrEndwmtFundGrp/EndYearBalanceAmt | 0 | 2559687 |
| IRS990ScheduleD/CYMinus4YrEndwmtFundGrp/GrantsOrScholarshipsAmt | 0 | 81600 |
| IRS990ScheduleD/CYMinus4YrEndwmtFundGrp/InvestmentEarningsOrLossesAmt | 0 | 35592 |
| IRS990ScheduleD/EndowmentsHeldRelatedOrgInd | 0 | 0 |
| IRS990ScheduleD/EndowmentsHeldUnrelatedOrgInd | 0 | 0 |
| IRS990ScheduleD/TotalBookValueLandBuildingsAmt | 0 | 0 |
| IRS990ScheduleI/GrantRecordsMaintainedInd | 0 | 1 |
| IRS990ScheduleI/RecipientTable/CashGrantAmt | 0 | 0 |
| IRS990ScheduleI/RecipientTable/IRCSectionDesc | 0 | 501(C)(3) |
| IRS990ScheduleI/RecipientTable/NonCashAssistanceAmt | 0 | 132000 |
| IRS990ScheduleI/RecipientTable/PurposeOfGrantTxt | 0 | OPERATIONS |
| IRS990ScheduleI/RecipientTable/RecipientBusinessName/BusinessNameLine1Txt | 0 | MILL VALLEY PUBLIC LIBRARY |
| IRS990ScheduleI/RecipientTable/RecipientEIN | 0 | 946000372 |
| IRS990ScheduleI/RecipientTable/USAddress/AddressLine1Txt | 0 | 375 THROCKMORTON AVE |
| IRS990ScheduleI/RecipientTable/USAddress/CityNm | 0 | MILL VALLEY |
| IRS990ScheduleI/RecipientTable/USAddress/StateAbbreviationCd | 0 | CA |
| IRS990ScheduleI/RecipientTable/USAddress/ZIPCd | 0 | 94941 |
| IRS990ScheduleI/RecipientTable/ValuationMethodUsedDesc | 0 | CASH |
| IRS990/ScheduleJRequiredInd | 0 | 0 |
| IRS990/ScheduleORequiredInd | 0 | 1 |
| IRS990ScheduleO/SupplementalInformationDetail/ExplanationTxt | 0 | FORM 990 IS PREPARED BY AN OUTSIDE TAX PROFESSIONAL. THE FORM IS THEN REVIEWED BY CERTAIN MEMBERS OF THE BOARD OF DIRECTORS. THIS GROUP OF INDIVIDUALS THEN DISCUSSES THE CONTENTS OF THE RETURN WITH THE OUTSIDE TAX PROFESSIONAL. AFTER A FULL REVIEW (WITH MODIFICATIONS WHERE NECESSARY), THE FINAL VERSION OF THE TAX RETURN IS PROVIDED TO ALL MEMBERS OF THE ORGANIZATION'S VOTING BODY. AN OFFICER SIGNS THE AUTHORIZATION FOR THE TAX PROFESSIONAL TO EFILE THE RETURN WITH THE DEPARTMENT OF THE TREASURY. |
| IRS990ScheduleO/SupplementalInformationDetail/ExplanationTxt | 1 | THE ORGANIZATION'S TAX FILINGS ARE STORED IN A SECURE ENVIRONMENT AND HELD AVAILABLE FOR INSPECTION BY TAX AUTHORITIES AND THE GENERAL PUBLIC UPON WRITTEN REQUEST TO THE ADDRESS OF THE MILL VALLEY LIBRARY FOUNDATION. |
| IRS990ScheduleO/SupplementalInformationDetail/ExplanationTxt | 2 | GOVERNING DOCUMENTS, POLICIES AND FINANCAL INFORMATION IS AVAILABLE UPON WRITTEN REQUEST TO THE ADDRESS OF THE MILL VALLEY LIBRARY FOUNDATION. |
| IRS990ScheduleO/SupplementalInformationDetail/ExplanationTxt | 3 | OTHER: PROGRAM SERVICE EXPENSES 0. MANAGEMENT AND GENERAL EXPENSES 36,548. FUNDRAISING EXPENSES 1,061. TOTAL EXPENSES 37,609. |
| IRS990ScheduleO/SupplementalInformationDetail/FormAndLineReferenceDesc | 0 | FORM 990, PART VI, SECTION B, LINE 11B |
| IRS990ScheduleO/SupplementalInformationDetail/FormAndLineReferenceDesc | 1 | FORM 990, PART VI, SECTION C, LINE 18 |
| IRS990ScheduleO/SupplementalInformationDetail/FormAndLineReferenceDesc | 2 | FORM 990, PART VI, SECTION C, LINE 19 |
| IRS990ScheduleO/SupplementalInformationDetail/FormAndLineReferenceDesc | 3 | FORM 990, PART IX, LINE 11G |
| IRS990ScheduleR/AssetExchangeInd | 0 | 0 |
| IRS990ScheduleR/AssetPurchaseFromOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/AssetSaleToOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/DivRelatedOrganizationInd | 0 | 0 |
| IRS990ScheduleR/GiftGrntCapContriFromOthOrgInd | 0 | 0 |
| IRS990ScheduleR/GiftGrntOrCapContriToOthOrgInd | 0 | 1 |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/ControlledOrganizationInd | 0 | 0 |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/DirectControllingNACd | 0 | N/A |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/DisregardedEntityName/BusinessNameLine1Txt | 0 | MILL VALLEY PUBLIC LIBRARY |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/EIN | 0 | 966000372 |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/ExemptCodeSectionTxt | 0 | 501(C)(3) |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/LegalDomicileStateCd | 0 | CA |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/PrimaryActivitiesTxt | 0 | LIBRARY |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/PublicCharityStatusTxt | 0 | 6 |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/USAddress/AddressLine1Txt | 0 | 375 THROCKMORTON AVENUE |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/USAddress/CityNm | 0 | MILL VALLEY |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/USAddress/StateAbbreviationCd | 0 | CA |
| IRS990ScheduleR/IdRelatedTaxExemptOrgGrp/USAddress/ZIPCd | 0 | 94941 |
| IRS990ScheduleR/LoansOrGuaranteesFromOthOrgInd | 0 | 0 |
| IRS990ScheduleR/LoansOrGuaranteesToOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/PaidEmployeesSharingInd | 0 | 0 |
| IRS990ScheduleR/PerformOfServicesByOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/PerformOfServicesForOthOrgInd | 0 | 0 |
| IRS990ScheduleR/ReceiptOfIntAnntsRntsRyltsInd | 0 | 0 |
| IRS990ScheduleR/ReimbursementPaidByOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/ReimbursementPaidToOtherOrgInd | 0 | 0 |
| IRS990ScheduleR/RentalOfFacilitiesToOthOrgInd | 0 | 0 |
| IRS990ScheduleR/RentalOfFcltsFromOthOrgInd | 0 | 0 |
| IRS990ScheduleR/SharingOfFacilitiesInd | 0 | 0 |
| IRS990ScheduleR/TransactionsRelatedOrgGrp/MethodOfAmountDeterminationTxt | 0 | POLICY |
| IRS990ScheduleR/TransactionsRelatedOrgGrp/OtherOrganizationName/BusinessNameLine1Txt | 0 | MILL VALLEY PUBLIC LIBRARY |
| IRS990ScheduleR/TransactionsRelatedOrgGrp/TransactionTypeTxt | 0 | B |
| IRS990ScheduleR/TransferFromOtherOrgInd | 0 | 0 |