2.4.0.84083 - Disclosure - Derivative Instruments (Details 4)truefalseIn Thousands, unless otherwise specifiedfalse1false USDtruefalse$I2013Q2_NondesignatedMemberhttp://www.sec.gov/CIK0001465885instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseDerivative instruments not accounted as hedges under GAAPus-gaap_HedgingDesignationAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NondesignatedMemberus-gaap_HedgingDesignationAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$2false USDtruefalse$I2012_NondesignatedMemberhttp://www.sec.gov/CIK0001465885instant2012-12-31T00:00:000001-01-01T00:00:00falsefalseDerivative instruments not accounted as hedges under GAAPus-gaap_HedgingDesignationAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NondesignatedMemberus-gaap_HedgingDesignationAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$3false USDtruefalse$I2013Q2_ToBeAnnouncedSecuritiesMember_NondesignatedMemberhttp://www.sec.gov/CIK0001465885instant2013-06-30T00:00:000001-01-01T00:00:00falsefalseTBA securitiesus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwmc_ToBeAnnouncedSecuritiesMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberfalsefalseDerivative instruments not accounted as hedges under GAAPus-gaap_HedgingDesignationAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NondesignatedMemberus-gaap_HedgingDesignationAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$4false USDtruefalse$D2013Q2YTD_ToBeAnnouncedSecuritiesMember_NondesignatedMember_LongMemberhttp://www.sec.gov/CIK0001465885duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseTBA securitiesus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwmc_ToBeAnnouncedSecuritiesMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberfalsefalseDerivative instruments not accounted as hedges under GAAPus-gaap_HedgingDesignationAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NondesignatedMemberus-gaap_HedgingDesignationAxisexplicitMemberfalsefalsePurchase contractswmc_PositionAxisxbrldihttp://xbrl.org/2006/xbrldiwmc_LongMemberwmc_PositionAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$5false USDtruefalse$D2013Q2YTD_ToBeAnnouncedSecuritiesMember_NondesignatedMember_ShortMemberhttp://www.sec.gov/CIK0001465885duration2013-01-01T00:00:002013-06-30T00:00:00falsefalseTBA securitiesus-gaap_DerivativeInstrumentRiskAxisxbrldihttp://xbrl.org/2006/xbrldiwmc_ToBeAnnouncedSecuritiesMemberus-gaap_DerivativeInstrumentRiskAxisexplicitMemberfalsefalseDerivative instruments not accounted as hedges under GAAPus-gaap_HedgingDesignationAxisxbrldihttp://xbrl.org/2006/xbrldius-gaap_NondesignatedMemberus-gaap_HedgingDesignationAxisexplicitMemberfalsefalseSale contractswmc_PositionAxisxbrldihttp://xbrl.org/2006/xbrldiwmc_ShortMemberwmc_PositionAxisexplicitMemberUSDStandardhttp://www.xbrl.org/2003/iso4217USDiso42170USDUSD$1true 4wmc_DerivativeNotionalAmountRollForwardwmc_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4falsefalsefalse00falsefalsefalse5falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Changes in notional amount2false 5invest_DerivativeNotionalAmountinvest_falsenainstantfalsefalsefalsefalsefalsetruefalsefalseperiodStartLabel1truefalsefalse41232030004123203USD$falsetruefalse2truefalsefalse41818000004181800USD$falsetruefalse3truefalsefalse500000000500000USD$falsetruefalse4truefalsefalse425000000425000USD$falsetruefalse5truefalsefalse425000000425000USD$falsetruefalsexbrli:monetaryItemTypemonetaryAggregate notional amount specified by the derivative(s). Expressed as an absolute value.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B false2Notional Amount at the beginning of the period3false 5wmc_DerivativeNotionalAmountAdditionswmc_falsedebitdurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4truefalsefalse16490000001649000falsefalsefalse5truefalsefalse22250000002225000falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the addition to total monetary amount specified by the derivative asset(s). Expressed as an absolute value.No definition available.false2Additions4false 5wmc_DerivativeNotionalAmountTerminatedAndSettledwmc_falsecreditdurationfalsefalsefalsefalsefalsefalsefalsetruenegatedLabel1falsefalsefalse00falsefalsefalse2falsefalsefalse00falsefalsefalse3falsefalsefalse00falsefalsefalse4truefalsefalse-1974000000-1974000falsefalsefalse5truefalsefalse-2050000000-2050000falsefalsefalsexbrli:monetaryItemTypemonetaryRepresents the aggregate termination value of derivative contracts, upon settlement that were terminated, settled or expired during the period.No definition available.false2Settlement, Termination, Expiration or Exercise5false 5invest_DerivativeNotionalAmountinvest_falsenainstantfalsefalsefalsefalsefalsefalsetruefalseperiodEndLabel1truefalsefalse41232030004123203USD$falsetruefalse2truefalsefalse41818000004181800USD$falsetruefalse3truefalsefalse500000000500000USD$falsetruefalse4truefalsefalse100000000100000USD$falsetruefalse5truefalsefalse600000000600000USD$falsetruefalsexbrli:monetaryItemTypemonetaryAggregate notional amount specified by the derivative(s). Expressed as an absolute value.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B false2Notional Amount at the end of the periodfalseDerivative Instruments (Details 4) (Derivative instruments not accounted as hedges under GAAP, USD $)ThousandsUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.westernassetmcc.com/role/DisclosureDerivativeInstrumentsDetails455