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| IRS990/AccountsPayableAccrExpnssGrp/EOYAmt | 0 | 1134931 |
| IRS990/AccountsReceivableGrp/BOYAmt | 0 | 92530 |
| IRS990/AccountsReceivableGrp/EOYAmt | 0 | 25837 |
| IRS990/ActivitiesConductedPrtshpInd | 0 | 0 |
| IRS990/ActivityOrMissionDesc | 0 | THE ORGANIZATION PROVIDES A COLLEGE PREPARATORY EDUCATION IN A COEDUCATIONAL ENVIRONMENT. |
| IRS990/AdvertisingGrp/ManagementAndGeneralAmt | 0 | 308747 |
| IRS990/AdvertisingGrp/TotalAmt | 0 | 308747 |
| IRS990/AllOtherContributionsAmt | 0 | 622530 |
| IRS990/AllOtherExpensesGrp/FundraisingAmt | 0 | 3568 |
| IRS990/AllOtherExpensesGrp/ManagementAndGeneralAmt | 0 | 118381 |
| IRS990/AllOtherExpensesGrp/ProgramServicesAmt | 0 | 71818 |
| IRS990/AllOtherExpensesGrp/TotalAmt | 0 | 193767 |
| IRS990/AnnualDisclosureCoveredPrsnInd | 0 | 1 |
| IRS990/AuditCommitteeInd | 0 | 1 |
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| IRS990/BooksInCareOfDetail/PhoneNum | 0 | 5088532640 |
| IRS990/BooksInCareOfDetail/USAddress/AddressLine1Txt | 0 | BANCROFT SCHOOL 110 SHORE DRIVE |
| IRS990/BooksInCareOfDetail/USAddress/CityNm | 0 | WORCESTER |
| IRS990/BooksInCareOfDetail/USAddress/StateAbbreviationCd | 0 | MA |
| IRS990/BooksInCareOfDetail/USAddress/ZIPCd | 0 | 01605 |
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| IRS990/BusinessRlnWithOrgMemInd | 0 | 0 |
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| IRS990/CashNonInterestBearingGrp/EOYAmt | 0 | 257951 |
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| IRS990/CompDisqualPersonsGrp/ProgramServicesAmt | 0 | 6106199 |
| IRS990/CompDisqualPersonsGrp/TotalAmt | 0 | 8772413 |
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| IRS990/CompensationProcessCEOInd | 0 | 1 |
| IRS990/CompensationProcessOtherInd | 0 | 1 |
| IRS990/ConflictOfInterestPolicyInd | 0 | 1 |
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| IRS990/CYContributionsGrantsAmt | 0 | 622530 |
| IRS990/CYGrantsAndSimilarPaidAmt | 0 | 4536786 |
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| IRS990/CYOtherRevenueAmt | 0 | -102716 |
| IRS990/CYProgramServiceRevenueAmt | 0 | 16283675 |
| IRS990/CYRevenuesLessExpensesAmt | 0 | -2979279 |
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| IRS990/CYTotalExpensesAmt | 0 | 20982469 |
| IRS990/CYTotalFundraisingExpenseAmt | 0 | 103194 |
| IRS990/CYTotalProfFndrsngExpnsAmt | 0 | 0 |
| IRS990/CYTotalRevenueAmt | 0 | 18003190 |
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| IRS990/DeferredRevenueGrp/EOYAmt | 0 | 2032040 |
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| IRS990/Desc | 0 | BANCROFT PROVIDES A COMPREHENSIVE, CARING, AND CREATIVE CURRICULAR AND EXTRACURRICULAR PROGRAM THAT FOSTERS AN EXPERIENCE OF EXCELLENCE FOR EACH STUDENT. INSPIRED STUDENTS, A SUPERIOR FACULTY, AND ENGAGED FAMILIES THRIVE IN OUR DIVERSE, SAFE, AND SUPPORTIVE COMMUNITY. WE AFFORD STUDENTS THE OPPORTUNITY TO DISCOVER THEIR PASSION IN LIFE AND TO LEARN TO EMBRACE CONFIDENTLY AND RESPONSIBLY THE MORAL AND ETHICAL CHALLENGES OF BEING LIFE-LONG LEARNERS, TEACHERS OF OTHERS, AND CITIZENS OF AN INCREASINGLY COMPLEX GLOBAL COMMUNITY. APPROXIMATELY 400 STUDENTS ATTEND BANCROFT. |
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| IRS990/DisregardedEntityInd | 0 | 0 |
| IRS990/DocumentRetentionPolicyInd | 0 | 1 |
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| IRS990/DonorRestrictionNetAssetsGrp/BOYAmt | 0 | 12704697 |
| IRS990/DonorRestrictionNetAssetsGrp/EOYAmt | 0 | 11728510 |
| IRS990/DonorRstrOrQuasiEndowmentsInd | 0 | 1 |
| IRS990/ElectionOfBoardMembersInd | 0 | 0 |
| IRS990/EmployeeCnt | 0 | 240 |
| IRS990/EmploymentTaxReturnsFiledInd | 0 | 0 |
| IRS990/EngagedInExcessBenefitTransInd | 0 | 0 |
| IRS990/EscrowAccountInd | 0 | 0 |
| IRS990/ExpenseAmt | 0 | 15825608 |
| IRS990/FamilyOrBusinessRlnInd | 0 | 0 |
| IRS990/FederalGrantAuditRequiredInd | 0 | 0 |
| IRS990/FeesForServicesAccountingGrp/ManagementAndGeneralAmt | 0 | 51651 |
| IRS990/FeesForServicesAccountingGrp/TotalAmt | 0 | 51651 |
| IRS990/FeesForServicesLegalGrp/ManagementAndGeneralAmt | 0 | 15431 |
| IRS990/FeesForServicesLegalGrp/TotalAmt | 0 | 15431 |
| IRS990/FeesForServicesOtherGrp/FundraisingAmt | 0 | 12368 |
| IRS990/FeesForServicesOtherGrp/ManagementAndGeneralAmt | 0 | 313333 |
| IRS990/FeesForServicesOtherGrp/ProgramServicesAmt | 0 | 14186 |
| IRS990/FeesForServicesOtherGrp/TotalAmt | 0 | 339887 |
| IRS990/FeesForSrvcInvstMgmntFeesGrp/ManagementAndGeneralAmt | 0 | 184972 |
| IRS990/FeesForSrvcInvstMgmntFeesGrp/TotalAmt | 0 | 184972 |
| IRS990/ForeignActivitiesInd | 0 | 0 |
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| IRS990/ForeignOfficeInd | 0 | 0 |
| IRS990/Form8282PropertyDisposedOfInd | 0 | 0 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 0 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 1 | 2.00 |
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| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 3 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 4 | 2.00 |
| 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/AverageHoursPerWeekRt | 15 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 16 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 17 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 18 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 19 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 20 | 2.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 21 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 22 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 23 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 24 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 25 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 26 | 40.00 |
| IRS990/Form990PartVIISectionAGrp/AverageHoursPerWeekRt | 27 | 40.00 |
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| IRS990/Form990PartVIISectionAGrp/HighestCompensatedEmployeeInd | 1 | X |
| IRS990/Form990PartVIISectionAGrp/HighestCompensatedEmployeeInd | 2 | X |
| IRS990/Form990PartVIISectionAGrp/HighestCompensatedEmployeeInd | 3 | X |
| 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/IndividualTrusteeOrDirectorInd | 15 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 16 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 17 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 18 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 19 | X |
| IRS990/Form990PartVIISectionAGrp/IndividualTrusteeOrDirectorInd | 20 | X |
| IRS990/Form990PartVIISectionAGrp/KeyEmployeeInd | 0 | 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 |
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| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 1 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 2 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 3 | 0 |
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| 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 |
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| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 14 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 15 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 16 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 17 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 18 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 19 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 20 | 0 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 21 | 26935 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 22 | 9334 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 23 | 30689 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 24 | 5494 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 25 | 13298 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 26 | 16955 |
| IRS990/Form990PartVIISectionAGrp/OtherCompensationAmt | 27 | 23234 |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 0 | WARNER FLETCHER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 1 | KHURSTON ELLIA-EPPLE |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 2 | SETH GARFIELD |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 3 | MARTIN RICHMAN |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 4 | JENNIFER VUONA |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 5 | NEIL MCDONOUGH |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 6 | KEVIN RAMOS-GLEW |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 7 | PETER JANHUNEN |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 8 | JYOTI DATTA |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 9 | PADGETT BERTHIAUME |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 10 | KATY SULLIVAN |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 11 | CAITLIN MCDONOUGH |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 12 | SOLON KELLEHER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 13 | SUSANNE CHOATE |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 14 | ASHLEY DONOHUE |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 15 | WILLIAM ZUJEWSKI |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 16 | JOSEPHINE HERRON TRUESDELL |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 17 | JAMES CONDON |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 18 | MICHAEL PALERMO |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 19 | BEN DOBSON |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 20 | MARY HALPIN CARTER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 21 | STEPHANIE LEUBBERS |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 22 | SCOTT POTTBECKER |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 23 | MARK TAYLOR |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 24 | GARTH ADAMS |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 25 | CRAIG JONES |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 26 | JACOB DIBBERT |
| IRS990/Form990PartVIISectionAGrp/PersonNm | 27 | DANIEL MERCURIO |
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| 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/ReportableCompFromOrgAmt | 15 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 16 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 17 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 18 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 19 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 20 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 21 | 281760 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 22 | 156878 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 23 | 118425 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 24 | 108995 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 25 | 126749 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 26 | 141149 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromOrgAmt | 27 | 109256 |
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| 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/ReportableCompFromRltdOrgAmt | 15 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 16 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 17 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 18 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 19 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 20 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 21 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 22 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 23 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 24 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 25 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 26 | 0 |
| IRS990/Form990PartVIISectionAGrp/ReportableCompFromRltdOrgAmt | 27 | 0 |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 0 | HONORARY TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 1 | VICE PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 2 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 3 | PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 4 | PFA PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 5 | HONORARY TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 6 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 7 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 8 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 9 | FIRST VICE PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 10 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 11 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 12 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 13 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 14 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 15 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 16 | ALUMNI COUNCIL PRESIDENT |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 17 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 18 | TREASURER |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 19 | SECRETARY |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 20 | TRUSTEE |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 21 | HEAD OF SCHOOL |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 22 | DIRECTOR OF OPERATIONS AND |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 23 | UPPER SCHOOL DIVISION HEAD |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 24 | DIRECTOR OF ATHLETICS |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 25 | DIRECTOR OF DIVERSITY, EQUITY, INCLUSION, & BELONG |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 26 | ASSISTANT HEAD OF SCH |
| IRS990/Form990PartVIISectionAGrp/TitleTxt | 27 | ASSISTANT HEAD OF SCH |
| IRS990/Form990ProvidedToGvrnBodyInd | 0 | 1 |
| IRS990/Form990TFiledInd | 0 | 1 |
| IRS990/FormationYr | 0 | 1902 |
| IRS990/FormerOfcrEmployeesListedInd | 0 | 1 |
| IRS990/FSAuditedBasisGrp/SeparateBasisFinclStmtInd | 0 | X |
| IRS990/FSAuditedInd | 0 | 1 |
| IRS990/FundraisingActivitiesInd | 0 | 0 |
| IRS990/GainOrLossGrp/SecuritiesAmt | 0 | 533276 |
| IRS990/GamingActivitiesInd | 0 | 0 |
| IRS990/GoverningBodyVotingMembersCnt | 0 | 21 |
| IRS990/GrantAmt | 0 | 4536786 |
| IRS990/GrantsToDomesticIndividualsGrp/ProgramServicesAmt | 0 | 4536786 |
| IRS990/GrantsToDomesticIndividualsGrp/TotalAmt | 0 | 4536786 |
| IRS990/GrantsToIndividualsInd | 0 | 1 |
| IRS990/GrantsToOrganizationsInd | 0 | 0 |
| IRS990/GrantToRelatedPersonInd | 0 | 0 |
| IRS990/GrossAmountSalesAssetsGrp/SecuritiesAmt | 0 | 16880856 |
| IRS990/GrossReceiptsAmt | 0 | 34772349 |
| IRS990/GrossRentsGrp/RealAmt | 0 | 225660 |
| IRS990/GrossSalesOfInventoryAmt | 0 | 47786 |
| IRS990/GroupReturnForAffiliatesInd | 0 | 0 |
| IRS990/IncludeFIN48FootnoteInd | 0 | 0 |
| IRS990/IndependentAuditFinclStmtInd | 0 | 1 |
| IRS990/IndependentVotingMemberCnt | 0 | 21 |
| IRS990/IndivRcvdGreaterThan100KCnt | 0 | 7 |
| IRS990/IndoorTanningServicesInd | 0 | 0 |
| IRS990/InfoInScheduleOPartVIInd | 0 | X |
| IRS990/InsuranceGrp/ManagementAndGeneralAmt | 0 | 8670 |
| IRS990/InsuranceGrp/ProgramServicesAmt | 0 | 78030 |
| IRS990/InsuranceGrp/TotalAmt | 0 | 86700 |
| IRS990/InterestGrp/ManagementAndGeneralAmt | 0 | 128046 |
| IRS990/InterestGrp/TotalAmt | 0 | 128046 |
| IRS990/InventoriesForSaleOrUseGrp/BOYAmt | 0 | 99625 |
| IRS990/InventoriesForSaleOrUseGrp/EOYAmt | 0 | 90377 |
| IRS990/InvestmentIncomeGrp/ExclusionAmt | 0 | 666425 |
| IRS990/InvestmentIncomeGrp/TotalRevenueColumnAmt | 0 | 666425 |
| IRS990/InvestmentInJointVentureInd | 0 | 0 |
| IRS990/InvestmentsOtherSecuritiesGrp/BOYAmt | 0 | 2248250 |
| IRS990/InvestmentsOtherSecuritiesGrp/EOYAmt | 0 | 1925128 |
| IRS990/InvestmentsPubTradedSecGrp/BOYAmt | 0 | 20379722 |
| IRS990/InvestmentsPubTradedSecGrp/EOYAmt | 0 | 19713872 |
| IRS990/InvestTaxExemptBondsInd | 0 | 0 |
| IRS990/IRPDocumentCnt | 0 | 100 |
| IRS990/IRPDocumentW2GCnt | 0 | 0 |
| IRS990/LandBldgEquipAccumDeprecAmt | 0 | 22544882 |
| IRS990/LandBldgEquipBasisNetGrp/BOYAmt | 0 | 7983956 |
| IRS990/LandBldgEquipBasisNetGrp/EOYAmt | 0 | 7403738 |
| IRS990/LandBldgEquipCostOrOtherBssAmt | 0 | 29948620 |
| IRS990/LegalDomicileStateCd | 0 | MA |
| IRS990/LessCostOthBasisSalesExpnssGrp/SecuritiesAmt | 0 | 16347580 |
| IRS990/LessRentalExpensesGrp/RealAmt | 0 | 381965 |
| 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 | BANCROFT, AN INDEPENDENT, COEDUCATIONAL, COLLEGE-PREPARATORY DAY SCHOOL, PREPARES TALENTED, WELL-QUALIFIED AND MOTIVATED COLLEGE-BOUND STUDENTS, PRE-KINDERGARTEN THROUGH GRADE 12, TO PURSUE AND REALIZE THEIR ACADEMIC, PERSONAL AND SOCIAL POTENTIAL. |
| IRS990/MoreThan5000KToIndividualsInd | 0 | 0 |
| IRS990/MoreThan5000KToOrgInd | 0 | 0 |
| IRS990/MortgNotesPyblScrdInvstPropGrp/BOYAmt | 0 | 9577529 |
| IRS990/MortgNotesPyblScrdInvstPropGrp/EOYAmt | 0 | 8498802 |
| IRS990/NetAssetsOrFundBalancesBOYAmt | 0 | 20138749 |
| IRS990/NetAssetsOrFundBalancesEOYAmt | 0 | 18211368 |
| IRS990/NetGainOrLossInvestmentsGrp/RelatedOrExemptFuncIncomeAmt | 0 | 533276 |
| IRS990/NetGainOrLossInvestmentsGrp/TotalRevenueColumnAmt | 0 | 533276 |
| IRS990/NetIncomeOrLossGrp/RelatedOrExemptFuncIncomeAmt | 0 | 8172 |
| IRS990/NetIncomeOrLossGrp/TotalRevenueColumnAmt | 0 | 8172 |
| IRS990/NetRentalIncomeOrLossGrp/TotalRevenueColumnAmt | 0 | -156305 |
| IRS990/NetRentalIncomeOrLossGrp/UnrelatedBusinessRevenueAmt | 0 | -156305 |
| IRS990/NetUnrelatedBusTxblIncmAmt | 0 | 0 |
| IRS990/NetUnrlzdGainsLossesInvstAmt | 0 | 1051897 |
| IRS990/NoDonorRestrictionNetAssetsGrp/BOYAmt | 0 | 7434052 |
| IRS990/NoDonorRestrictionNetAssetsGrp/EOYAmt | 0 | 6482858 |
| IRS990/NondeductibleContributionsInd | 0 | 0 |
| IRS990/OccupancyGrp/ManagementAndGeneralAmt | 0 | 266947 |
| IRS990/OccupancyGrp/ProgramServicesAmt | 0 | 849921 |
| IRS990/OccupancyGrp/TotalAmt | 0 | 1116868 |
| IRS990/OfficeExpensesGrp/FundraisingAmt | 0 | 850 |
| IRS990/OfficeExpensesGrp/ManagementAndGeneralAmt | 0 | 10084 |
| IRS990/OfficeExpensesGrp/TotalAmt | 0 | 10934 |
| IRS990/OfficerMailingAddressInd | 0 | 0 |
| IRS990/OnBehalfOfIssuerInd | 0 | 0 |
| IRS990/OperateHospitalInd | 0 | 0 |
| IRS990/Organization501c3Ind | 0 | X |
| IRS990/OrganizationFollowsFASB117Ind | 0 | X |
| IRS990/OtherChangesInNetAssetsAmt | 0 | 0 |
| IRS990/OtherEmployeeBenefitsGrp/ManagementAndGeneralAmt | 0 | 326316 |
| IRS990/OtherEmployeeBenefitsGrp/ProgramServicesAmt | 0 | 531481 |
| IRS990/OtherEmployeeBenefitsGrp/TotalAmt | 0 | 857797 |
| IRS990/OtherExpensesGrp/Desc | 0 | CLASSROOM SUPPLIES |
| IRS990/OtherExpensesGrp/Desc | 1 | EDUCATIONAL PROGRAMS |
| IRS990/OtherExpensesGrp/Desc | 2 | MISCELLANEOUS |
| IRS990/OtherExpensesGrp/Desc | 3 | SECURITY |
| IRS990/OtherExpensesGrp/FundraisingAmt | 0 | 1755 |
| IRS990/OtherExpensesGrp/FundraisingAmt | 1 | 84653 |
| IRS990/OtherExpensesGrp/ManagementAndGeneralAmt | 0 | 23816 |
| IRS990/OtherExpensesGrp/ManagementAndGeneralAmt | 1 | 154544 |
| IRS990/OtherExpensesGrp/ProgramServicesAmt | 0 | 1137006 |
| IRS990/OtherExpensesGrp/ProgramServicesAmt | 1 | 523824 |
| IRS990/OtherExpensesGrp/ProgramServicesAmt | 2 | 16814 |
| IRS990/OtherExpensesGrp/ProgramServicesAmt | 3 | 167809 |
| IRS990/OtherExpensesGrp/TotalAmt | 0 | 1162577 |
| IRS990/OtherExpensesGrp/TotalAmt | 1 | 523824 |
| IRS990/OtherExpensesGrp/TotalAmt | 2 | 256011 |