2.4.0.8019 - Disclosure - Investments in Local Limited Partnerships (Details)truefalsefalse1false USDfalsefalse$Context_As_Of_31-Mar-2013http://www.sec.gov/CIK0000911568instant2013-03-31T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDfalsefalse$Context_As_Of_31-Mar-2012http://www.sec.gov/CIK0000911568instant2012-03-31T00:00:000001-01-01T00:00:00USDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1false 4bftcviii_CapitalContributionsAndAdvancesPaidToLocalLimitedPartnershipsbftcviii_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse40153764015376USD$falsetruefalse2truefalsefalse1594319615943196USD$falsetruefalsexbrli:monetaryItemTypemonetaryCapital contributions and advances made to local limited partnership investments as of balance sheet date.No definition available.false2Capital contributions and advances paid to Local Limited Partnerships2false 4bftcviii_CumulativeEquityInLossesOfLocalLimitedPartnershipRecognizedbftcviii_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse-2971814-2971814falsefalsefalse2truefalsefalse-8813573-8813573falsefalsefalsexbrli:monetaryItemTypemonetaryThis item represents the cumulative equity in losses of local limited partnership investments as of balance sheet date.No definition available.false2Cumulative equity in losses of Local Limited Partnerships (excluding cumulative unrecognized losses of $945,515 and $3,202,928 at March 31, 2013 and 2012, respectively)3false 4bftcviii_CumulativeCashDistributionsReceivedFromLimitedPartnershipsbftcviii_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse-43323-43323falsefalsefalse2truefalsefalse-480795-480795falsefalsefalsexbrli:monetaryItemTypemonetaryThis item represents cumulative cash distributions received from limited partnership investments as of balance sheet date.No definition available.false2Cumulative cash distributions received from Local Limited Partnerships4false 4bftcviii_InvestmentsInLocalLimitedPartnershipsBeforeAdjustmentsbftcviii_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse10002391000239falsefalsefalse2truefalsefalse66488286648828falsefalsefalsexbrli:monetaryItemTypemonetaryTotal investments in local limited partnership before adjustments as of balance sheet date.No definition available.true2Investments in Local Limited Partnerships before adjustments5true 4bftcviii_ExcessInvestmentCostsOverUnderlyingAssetsAcquiredAbstractbftcviii_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Excess investment costs over the underlying assets acquired:6false 5bftcviii_AcquisitionFeesAndExpensesbftcviii_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalseverboseLabel1truefalsefalse4989249892falsefalsefalse2truefalsefalse619931619931falsefalsefalsexbrli:monetaryItemTypemonetaryThe cumulative amount recorded pertaining to the acquisition fees and expenses as of balance sheet date.No definition available.false2Acquisition fees and expenses7false 5bftcviii_CumulativeAmortizationOfAcquisitionFeesAndExpensesbftcviii_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse-15131-15131falsefalsefalse2truefalsefalse-187865-187865falsefalsefalsexbrli:monetaryItemTypemonetaryThe cumulative amount recorded pertaining to amortization of acquisition fees and expenses as of balance sheet date.No definition available.false2Cumulative amortization of acquisition fees and expenses8false 5bftcviii_InvestmentsInLocalLimitedPartnershipsBeforeValuationAllowanceAndImpairmentbftcviii_falsedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse10350001035000falsefalsefalse2truefalsefalse70808947080894falsefalsefalsexbrli:monetaryItemTypemonetaryThe carrying value of investment recorded as of the balance sheet date pertaining to Investments in Local Limited Partnerships before valuation allowance as of balance sheet date.No definition available.true2Investments in Local Limited Partnerships before valuation allowance and impairment9false 5bftcviii_CumulativeValuationAllowanceOnAdvancesToLocalLimitedPartnershipsbftcviii_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse00falsefalsefalse2truefalsefalse-1417455-1417455falsefalsefalsexbrli:monetaryItemTypemonetaryThe cumulative amount recorded pertaining to valuation allowance on advances to Local Limited partnership as of balance sheet date.No definition available.false2Cumulative valuation allowance on advances to Local Limited Partnerships10false 5bftcviii_CumulativeImpairmentOnInvestmentsInLocalLimitedPartnershipsbftcviii_falsecreditinstantfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1truefalsefalse-1035000-1035000falsefalsefalse2truefalsefalse-3663000-3663000falsefalsefalsexbrli:monetaryItemTypemonetaryThe cumulative amount recorded pertaining to impairment on Local Limited partnership investment as of balance sheet date.No definition available.false2Cumulative impairment on investments in Local Limited Partnerships11false 4us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVenturesus-gaap_truedebitinstantfalsefalsefalsefalsefalsefalsefalsefalsetotalLabel1truefalsefalse00USD$falsetruefalse2truefalsefalse20004392000439USD$falsetruefalsexbrli:monetaryItemTypemonetaryTotal investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 true2Investments in Local Limited PartnershipsfalseInvestments in Local Limited Partnerships (Details) (USD $)NoRoundingUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.bostonfinancial.com/role/InvestmentsInLocalLimitedPartnershipsDetails211