3.19.3.a.u2 html 1170 529 1 false 235 0 false 9 false false R1.htm 0001000 - Document - Document and Entity Information Sheet http://www.westernasset.com/role/DocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 1001000 - Statement - Consolidated Balance Sheets Sheet http://www.westernasset.com/role/ConsolidatedBalanceSheets Consolidated Balance Sheets Statements 2 false false R3.htm 1001501 - Statement - Consolidated Balance Sheets (Parenthetical) Sheet http://www.westernasset.com/role/ConsolidatedBalanceSheetsParenthetical Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 1002000 - Statement - Consolidated Statements of Operations Sheet http://www.westernasset.com/role/ConsolidatedStatementsOfOperations Consolidated Statements of Operations Statements 4 false false R5.htm 1002001 - Statement - Consolidated Statements of Operations (Parenthetical) Sheet http://www.westernasset.com/role/ConsolidatedStatementsOfOperationsParenthetical Consolidated Statements of Operations (Parenthetical) Statements 5 false false R6.htm 1003000 - Statement - Consolidated Statements of Changes in Stockholders' Equity Sheet http://www.westernasset.com/role/ConsolidatedStatementsOfChangesInStockholdersEquity Consolidated Statements of Changes in Stockholders' Equity Statements 6 false false R7.htm 1004000 - Statement - Consolidated Statements of Cash Flows Sheet http://www.westernasset.com/role/ConsolidatedStatementsOfCashFlows Consolidated Statements of Cash Flows Statements 7 false false R8.htm 2101100 - Disclosure - Organization Sheet http://www.westernasset.com/role/Organization Organization Notes 8 false false R9.htm 2102100 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies Sheet http://www.westernasset.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies Basis of Presentation and Summary of Significant Accounting Policies Notes 9 false false R10.htm 2103100 - Disclosure - Fair Value of Financial Instruments Sheet http://www.westernasset.com/role/FairValueOfFinancialInstruments Fair Value of Financial Instruments Notes 10 false false R11.htm 2104100 - Disclosure - Mortgage-Backed Securities and other securities Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecurities Mortgage-Backed Securities and other securities Notes 11 false false R12.htm 2105100 - Disclosure - Residential Whole Loans and Bridge Loans Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoans Residential Whole Loans and Bridge Loans Notes 12 false false R13.htm 2106100 - Disclosure - Commercial Loans Commercial Loans Sheet http://www.westernasset.com/role/CommercialLoansCommercialLoans Commercial Loans Commercial Loans Notes 13 false false R14.htm 2107100 - Disclosure - Financings Sheet http://www.westernasset.com/role/Financings Financings Notes 14 false false R15.htm 2108100 - Disclosure - Derivative Instruments Sheet http://www.westernasset.com/role/DerivativeInstruments Derivative Instruments Notes 15 false false R16.htm 2109100 - Disclosure - Offsetting Assets and Liabilities Sheet http://www.westernasset.com/role/OffsettingAssetsAndLiabilities Offsetting Assets and Liabilities Notes 16 false false R17.htm 2110100 - Disclosure - Related Party Transactions Sheet http://www.westernasset.com/role/RelatedPartyTransactions Related Party Transactions Notes 17 false false R18.htm 2111100 - Disclosure - Share-Based Payments Sheet http://www.westernasset.com/role/ShareBasedPayments Share-Based Payments Notes 18 false false R19.htm 2112100 - Disclosure - Stockholders' Equity Sheet http://www.westernasset.com/role/StockholdersEquity Stockholders' Equity Notes 19 false false R20.htm 2113100 - Disclosure - Net Income per Common Share Sheet http://www.westernasset.com/role/NetIncomePerCommonShare Net Income per Common Share Notes 20 false false R21.htm 2114100 - Disclosure - Income Taxes Sheet http://www.westernasset.com/role/IncomeTaxes Income Taxes Notes 21 false false R22.htm 2115100 - Disclosure - Contingencies Sheet http://www.westernasset.com/role/Contingencies Contingencies Notes 22 false false R23.htm 2116100 - Disclosure - Summarized Quarterly Results (unaudited) Sheet http://www.westernasset.com/role/SummarizedQuarterlyResultsUnaudited Summarized Quarterly Results (unaudited) Notes 23 false false R24.htm 2118100 - Disclosure - Subsequent Events Sheet http://www.westernasset.com/role/SubsequentEvents Subsequent Events Notes 24 false false R25.htm 2119100 - Disclosure - Schedule IV - Mortgage Loans on Real Estate Sheet http://www.westernasset.com/role/ScheduleIvMortgageLoansOnRealEstate Schedule IV - Mortgage Loans on Real Estate Notes 25 false false R26.htm 2202201 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies (Policies) Sheet http://www.westernasset.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesPolicies Basis of Presentation and Summary of Significant Accounting Policies (Policies) Policies http://www.westernasset.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPolicies 26 false false R27.htm 2302302 - Disclosure - Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Summary of Significant Accounting Policies (Tables) Sheet http://www.westernasset.com/role/BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesBasisOfPresentationAndSummaryOfSignificantAccountingPoliciesTables Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Summary of Significant Accounting Policies (Tables) Tables 27 false false R28.htm 2303301 - Disclosure - Fair Value of Financial Instruments (Tables) Sheet http://www.westernasset.com/role/FairValueOfFinancialInstrumentsTables Fair Value of Financial Instruments (Tables) Tables http://www.westernasset.com/role/FairValueOfFinancialInstruments 28 false false R29.htm 2304301 - Disclosure - Mortgage-Backed Securities and other securities (Tables) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesTables Mortgage-Backed Securities and other securities (Tables) Tables http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecurities 29 false false R30.htm 2305301 - Disclosure - Residential Whole Loans and Bridge Loans (Tables) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansTables Residential Whole Loans and Bridge Loans (Tables) Tables http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoans 30 false false R31.htm 2306301 - Disclosure - Commercial Loans (Tables) Sheet http://www.westernasset.com/role/CommercialLoansTables Commercial Loans (Tables) Tables http://www.westernasset.com/role/CommercialLoansCommercialLoans 31 false false R32.htm 2307301 - Disclosure - Financings (Tables) Sheet http://www.westernasset.com/role/FinancingsTables Financings (Tables) Tables http://www.westernasset.com/role/Financings 32 false false R33.htm 2308301 - Disclosure - Derivative Instruments (Tables) Sheet http://www.westernasset.com/role/DerivativeInstrumentsTables Derivative Instruments (Tables) Tables http://www.westernasset.com/role/DerivativeInstruments 33 false false R34.htm 2309301 - Disclosure - Offsetting Assets and Liabilities (Tables) Sheet http://www.westernasset.com/role/OffsettingAssetsAndLiabilitiesTables Offsetting Assets and Liabilities (Tables) Tables http://www.westernasset.com/role/OffsettingAssetsAndLiabilities 34 false false R35.htm 2311301 - Disclosure - Share-Based Payments (Tables) Sheet http://www.westernasset.com/role/ShareBasedPaymentsTables Share-Based Payments (Tables) Tables http://www.westernasset.com/role/ShareBasedPayments 35 false false R36.htm 2312301 - Disclosure - Stockholders' Equity (Tables) Sheet http://www.westernasset.com/role/StockholdersEquityTables Stockholders' Equity (Tables) Tables http://www.westernasset.com/role/StockholdersEquity 36 false false R37.htm 2313301 - Disclosure - Net Income per Common Share (Tables) Sheet http://www.westernasset.com/role/NetIncomePerCommonShareTables Net Income per Common Share (Tables) Tables http://www.westernasset.com/role/NetIncomePerCommonShare 37 false false R38.htm 2314301 - Disclosure - Income Taxes (Tables) Sheet http://www.westernasset.com/role/IncomeTaxesTables Income Taxes (Tables) Tables http://www.westernasset.com/role/IncomeTaxes 38 false false R39.htm 2316301 - Disclosure - Summarized Quarterly Results (unaudited) (Tables) Sheet http://www.westernasset.com/role/SummarizedQuarterlyResultsUnauditedTables Summarized Quarterly Results (unaudited) (Tables) Tables http://www.westernasset.com/role/SummarizedQuarterlyResultsUnaudited 39 false false R40.htm 2403402 - Disclosure - Fair Value of Financial Instruments (Details) Sheet http://www.westernasset.com/role/FairValueOfFinancialInstrumentsDetails Fair Value of Financial Instruments (Details) Details http://www.westernasset.com/role/FairValueOfFinancialInstrumentsTables 40 false false R41.htm 2403403 - Disclosure - Fair Value of Financial Instruments - Narrative (Details) Sheet http://www.westernasset.com/role/FairValueOfFinancialInstrumentsNarrativeDetails Fair Value of Financial Instruments - Narrative (Details) Details 41 false false R42.htm 2403404 - Disclosure - Fair Value of Financial Instruments - Summary of quantitative information (Details) Sheet http://www.westernasset.com/role/FairValueOfFinancialInstrumentsSummaryOfQuantitativeInformationDetails Fair Value of Financial Instruments - Summary of quantitative information (Details) Details 42 false false R43.htm 2403405 - Disclosure - Fair Value of Financial Instruments - Carrying Value and Estimated Fair Value of Financial Instruments (Details) Sheet http://www.westernasset.com/role/FairValueOfFinancialInstrumentsCarryingValueAndEstimatedFairValueOfFinancialInstrumentsDetails Fair Value of Financial Instruments - Carrying Value and Estimated Fair Value of Financial Instruments (Details) Details 43 false false R44.htm 2404402 - Disclosure - Mortgage-Backed Securities and other securities - Company's investment portfolio (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesCompanysInvestmentPortfolioDetails Mortgage-Backed Securities and other securities - Company's investment portfolio (Details) Details 44 false false R45.htm 2404403 - Disclosure - Mortgage-Backed Securities and other securities - Changes in the components of purchase discount and amortizable premium (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesChangesInComponentsOfPurchaseDiscountAndAmortizablePremiumDetails Mortgage-Backed Securities and other securities - Changes in the components of purchase discount and amortizable premium (Details) Details 45 false false R46.htm 2404404 - Disclosure - - Fair value and contractual maturities of the Company's investment securities (Details) Sheet http://www.westernasset.com/role/FairValueAndContractualMaturitiesOfCompanysInvestmentSecuritiesDetails - Fair value and contractual maturities of the Company's investment securities (Details) Details 46 false false R47.htm 2404405 - Disclosure - Mortgage-Backed Securities and other securities - Gross unrealized losses and estimated fair value (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesGrossUnrealizedLossesAndEstimatedFairValueDetails Mortgage-Backed Securities and other securities - Gross unrealized losses and estimated fair value (Details) Details 47 false false R48.htm 2404406 - Disclosure - Mortgage-Backed Securities and other securities - OTTI and Interest Income (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesOttiAndInterestIncomeDetails Mortgage-Backed Securities and other securities - OTTI and Interest Income (Details) Details 48 false false R49.htm 2404407 - Disclosure - Mortgage-Backed Securities and other securities - Sales and realized gains (losses) (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesSalesAndRealizedGainsLossesDetails Mortgage-Backed Securities and other securities - Sales and realized gains (losses) (Details) Details 49 false false R50.htm 2404408 - Disclosure - Mortgage-Backed Securities and other securities - Unconsolidated CMBS VIEs (Details) Sheet http://www.westernasset.com/role/MortgageBackedSecuritiesAndOtherSecuritiesUnconsolidatedCmbsViesDetails Mortgage-Backed Securities and other securities - Unconsolidated CMBS VIEs (Details) Details 50 false false R51.htm 2405402 - Disclosure - Residential (Details) Sheet http://www.westernasset.com/role/ResidentialDetails Residential (Details) Details http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansTables 51 false false R52.htm 2405403 - Disclosure - Residential Whole Loans and Bridge Loans Summary of the Assets and Liabilities (Details) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansSummaryOfAssetsAndLiabilitiesDetails Residential Whole Loans and Bridge Loans Summary of the Assets and Liabilities (Details) Details 52 false false R53.htm 2405404 - Disclosure - Residential Whole Loans and Bridge Loans Carrying Value Components (Details) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansCarryingValueComponentsDetails Residential Whole Loans and Bridge Loans Carrying Value Components (Details) Details 53 false false R54.htm 2405405 - Disclosure - Residential Whole Loans and Bridge Loans Investment Portfolio (Details) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansInvestmentPortfolioDetails Residential Whole Loans and Bridge Loans Investment Portfolio (Details) Details 54 false false R55.htm 2405406 - Disclosure - Residential Whole Loans and Bridge Loans Geographic Concentration (Details) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansGeographicConcentrationDetails Residential Whole Loans and Bridge Loans Geographic Concentration (Details) Details 55 false false R56.htm 2405407 - Disclosure - Residential Whole Loans and Bridge Loans Aging of Delinquent Loans (Details) Sheet http://www.westernasset.com/role/ResidentialWholeLoansAndBridgeLoansAgingOfDelinquentLoansDetails Residential Whole Loans and Bridge Loans Aging of Delinquent Loans (Details) Details 56 false false R57.htm 2406402 - Disclosure - Commercial Loans - Narrative (Details) Sheet http://www.westernasset.com/role/CommercialLoansNarrativeDetails Commercial Loans - Narrative (Details) Details 57 false false R58.htm 2406403 - Disclosure - Commercial Loans - Commercial loans held (Details) Sheet http://www.westernasset.com/role/CommercialLoansCommercialLoansHeldDetails Commercial Loans - Commercial loans held (Details) Details 58 false false R59.htm 2406404 - Disclosure - Commercial Loans - Consolidated trusts included in the Consolidated Balance Sheets (Details) Sheet http://www.westernasset.com/role/CommercialLoansConsolidatedTrustsIncludedInConsolidatedBalanceSheetsDetails Commercial Loans - Consolidated trusts included in the Consolidated Balance Sheets (Details) Details 59 false false R60.htm 2406405 - Disclosure - Commercial Loans - Components of the carrying value of the commercial real estate loans (Details) Sheet http://www.westernasset.com/role/CommercialLoansComponentsOfCarryingValueOfCommercialRealEstateLoansDetails Commercial Loans - Components of the carrying value of the commercial real estate loans (Details) Details 60 false false R61.htm 2407402 - Disclosure - Financings - Narrative (Details) Sheet http://www.westernasset.com/role/FinancingsNarrativeDetails Financings - Narrative (Details) Details 61 false false R62.htm 2407403 - Disclosure - Financings - Repurchase Agreements Remaining Maturities (Details) Sheet http://www.westernasset.com/role/FinancingsRepurchaseAgreementsRemainingMaturitiesDetails Financings - Repurchase Agreements Remaining Maturities (Details) Details 62 false false R63.htm 2407404 - Disclosure - Financings - Collateral at Risk Under its Repurchase Agreements Greater than 10% (Details) Sheet http://www.westernasset.com/role/FinancingsCollateralAtRiskUnderItsRepurchaseAgreementsGreaterThan10Details Financings - Collateral at Risk Under its Repurchase Agreements Greater than 10% (Details) Details 63 false false R64.htm 2407405 - Disclosure - Financings - Collateral Positions (Details) Sheet http://www.westernasset.com/role/FinancingsCollateralPositionsDetails Financings - Collateral Positions (Details) Details 64 false false R65.htm 2407406 - Disclosure - Financings - Convertible Senior Unsecured Notes (Details) Notes http://www.westernasset.com/role/FinancingsConvertibleSeniorUnsecuredNotesDetails Financings - Convertible Senior Unsecured Notes (Details) Details 65 false false R66.htm 2407407 - Disclosure - Financings - Commercial Mortgage Pass-Through Certificates (Details) Sheet http://www.westernasset.com/role/FinancingsCommercialMortgagePassThroughCertificatesDetails Financings - Commercial Mortgage Pass-Through Certificates (Details) Details 66 false false R67.htm 2408402 - Disclosure - Derivative Instruments- Summary (Details) Sheet http://www.westernasset.com/role/DerivativeInstrumentsSummaryDetails Derivative Instruments- Summary (Details) Details 67 false false R68.htm 2408403 - Disclosure - Derivative Instruments - Gains and Losses (Details) Sheet http://www.westernasset.com/role/DerivativeInstrumentsGainsAndLossesDetails Derivative Instruments - Gains and Losses (Details) Details 68 false false R69.htm 2408404 - Disclosure - Derivative Instruments - Interest Rate Swaps (Details) Sheet http://www.westernasset.com/role/DerivativeInstrumentsInterestRateSwapsDetails Derivative Instruments - Interest Rate Swaps (Details) Details 69 false false R70.htm 2408405 - Disclosure - Derivative Instruments- Currency Swaps and Forwards (Details) Sheet http://www.westernasset.com/role/DerivativeInstrumentsCurrencySwapsAndForwardsDetails Derivative Instruments- Currency Swaps and Forwards (Details) Details 70 false false R71.htm 2408406 - Disclosure - Derivative Instruments - TBAs (Details) Sheet http://www.westernasset.com/role/DerivativeInstrumentsTbasDetails Derivative Instruments - TBAs (Details) Details 71 false false R72.htm 2409402 - Disclosure - Offsetting Assets and Liabilities (Details) Sheet http://www.westernasset.com/role/OffsettingAssetsAndLiabilitiesDetails Offsetting Assets and Liabilities (Details) Details http://www.westernasset.com/role/OffsettingAssetsAndLiabilitiesTables 72 false false R73.htm 2410401 - Disclosure - Related Party Transactions (Details) Sheet http://www.westernasset.com/role/RelatedPartyTransactionsDetails Related Party Transactions (Details) Details http://www.westernasset.com/role/RelatedPartyTransactions 73 false false R74.htm 2411402 - Disclosure - Share-Based Payments (Details) Sheet http://www.westernasset.com/role/ShareBasedPaymentsDetails Share-Based Payments (Details) Details http://www.westernasset.com/role/ShareBasedPaymentsTables 74 false false R75.htm 2412402 - Disclosure - Stockholders' Equity (Details) Sheet http://www.westernasset.com/role/StockholdersEquityDetails Stockholders' Equity (Details) Details http://www.westernasset.com/role/StockholdersEquityTables 75 false false R76.htm 2413402 - Disclosure - Net Income per Common Share (Details) Sheet http://www.westernasset.com/role/NetIncomePerCommonShareDetails Net Income per Common Share (Details) Details http://www.westernasset.com/role/NetIncomePerCommonShareTables 76 false false R77.htm 2414402 - Disclosure - Income Taxes (Details) Sheet http://www.westernasset.com/role/IncomeTaxesDetails Income Taxes (Details) Details http://www.westernasset.com/role/IncomeTaxesTables 77 false false R78.htm 2414403 - Disclosure - Income Taxes Components of Income Tax Expense (Details) Sheet http://www.westernasset.com/role/IncomeTaxesComponentsOfIncomeTaxExpenseDetails Income Taxes Components of Income Tax Expense (Details) Details 78 false false R79.htm 2414404 - Disclosure - Income Taxes Deferred Tax Asset/Liability (Details) Sheet http://www.westernasset.com/role/IncomeTaxesDeferredTaxAssetLiabilityDetails Income Taxes Deferred Tax Asset/Liability (Details) Details 79 false false R80.htm 2414405 - Disclosure - Income Taxes Effective Income Tax Rate Reconciliation (Details) Sheet http://www.westernasset.com/role/IncomeTaxesEffectiveIncomeTaxRateReconciliationDetails Income Taxes Effective Income Tax Rate Reconciliation (Details) Details 80 false false R81.htm 2416402 - Disclosure - Summarized Quarterly Results (unaudited) (Details) Sheet http://www.westernasset.com/role/SummarizedQuarterlyResultsUnauditedDetails Summarized Quarterly Results (unaudited) (Details) Details http://www.westernasset.com/role/SummarizedQuarterlyResultsUnauditedTables 81 false false R82.htm 2419401 - Disclosure - Schedule IV Mortgage Loans on Real Estate (Details) Sheet http://www.westernasset.com/role/ScheduleIvMortgageLoansOnRealEstateDetails Schedule IV Mortgage Loans on Real Estate (Details) Details 82 false false All Reports Book All Reports wmc10k12312019.htm wmc-20191231.xsd wmc-20191231_cal.xml wmc-20191231_def.xml wmc-20191231_lab.xml wmc-20191231_pre.xml wmc12312019ex231.htm wmc12312019ex311.htm wmc12312019ex312.htm wmc12312019ex321.htm wmc12312019ex45.htm chart-26e2fb18f66a572fb68.jpg chart-8722cb306b675778835.jpg chart-aa7557fa08d351cd8f4.jpg logob31.gif http://xbrl.sec.gov/invest/2013-01-31 http://fasb.org/us-gaap/2018-01-31 http://xbrl.sec.gov/dei/2018-01-31 http://fasb.org/srt/2018-01-31 http://xbrl.sec.gov/stpr/2018-01-31 true true