2.4.0.6 Html 94 209 1 true 39 0 false 4 false false R1.htm 000 - Disclosure - Document And Entity Information Sheet http://na/role/DocumentAndEntityInformation Document And Entity Information true false R2.htm 001 - Statement - Condensed Balance Sheets (Unaudited) Sheet http://na/role/ConsolidatedBalanceSheet Condensed Balance Sheets (Unaudited) false false R3.htm 002 - Statement - Condensed Balance Sheets (Unaudited) (Parentheticals) Sheet http://na/role/ConsolidatedBalanceSheet_Parentheticals Condensed Balance Sheets (Unaudited) (Parentheticals) false false R4.htm 003 - Statement - Condensed Statement of Operations (Unaudited) Sheet http://na/role/ConsolidatedIncomeStatement Condensed Statement of Operations (Unaudited) false false R5.htm 004 - Statement - Condensed Statement of Comprehensive Income (Unaudited) Sheet http://na/role/ConsolidatedComprehensiveIncome Condensed Statement of Comprehensive Income (Unaudited) false false R6.htm 005 - Statement - Condensed Statement of Stockholders' Equity (Unaudited) Sheet http://na/role/ShareholdersEquityType2or3 Condensed Statement of Stockholders' Equity (Unaudited) false false R7.htm 006 - Statement - Condensed Statement of Cash Flows (Unaudited) Sheet http://na/role/ConsolidatedCashFlow Condensed Statement of Cash Flows (Unaudited) false false R8.htm 007 - Disclosure - Note 1 - Basis of Presentation Sheet http://na/role/Note Note 1 - Basis of Presentation false false R9.htm 008 - Disclosure - Note 2 - Organization and Nature of Business Operations Sheet http://na/role/Note0 Note 2 - Organization and Nature of Business Operations false false R10.htm 009 - Disclosure - Note 3 - Summary of Significant Accounting Policies Sheet http://na/role/Note00 Note 3 - Summary of Significant Accounting Policies false false R11.htm 010 - Disclosure - Note 4 - Recent Accounting Pronouncements Sheet http://na/role/Note000 Note 4 - Recent Accounting Pronouncements false false R12.htm 011 - Disclosure - Note 5 - Agency Securities, Available for Sale Sheet http://na/role/Note0000 Note 5 - Agency Securities, Available for Sale false false R13.htm 012 - Disclosure - Note 7 - Fair Value of Financial Instruments Sheet http://na/role/Note00000 Note 7 - Fair Value of Financial Instruments false false R14.htm 013 - Disclosure - Note 8 - Repurchase Agreements Sheet http://na/role/Note000000 Note 8 - Repurchase Agreements false false R15.htm 014 - Disclosure - Note 9 - Derivatives Sheet http://na/role/Note0000000 Note 9 - Derivatives false false R16.htm 015 - Disclosure - Note 10 - Share-Based Compensation Sheet http://na/role/Note00000000 Note 10 - Share-Based Compensation false false R17.htm 016 - Disclosure - Note 11 - Stockholders' Equity Sheet http://na/role/Note000000000 Note 11 - Stockholders' Equity false false R18.htm 017 - Disclosure - Note 12 - Net Income per Common Share Sheet http://na/role/Note0000000000 Note 12 - Net Income per Common Share false false R19.htm 018 - Disclosure - Note 13 - Income Taxes Sheet http://na/role/Note00000000000 Note 13 - Income Taxes false false R20.htm 019 - Disclosure - Note 14 - Commitments and Contingencies Sheet http://na/role/Note000000000000 Note 14 - Commitments and Contingencies false false R21.htm 020 - Disclosure - Note 15 - Related Party Transactions Sheet http://na/role/Note0000000000000 Note 15 - Related Party Transactions false false R22.htm 021 - Disclosure - Note 16 - Interest Rate Risk Sheet http://na/role/Note00000000000000 Note 16 - Interest Rate Risk false false R23.htm 022 - Disclosure - Note 17 - Subsequent events Sheet http://na/role/Note000000000000000 Note 17 - Subsequent events false false R24.htm 023 - Disclosure - Accounting Policies, by Policy (Policies) Sheet http://na/role/AccountingPoliciesByPolicy Accounting Policies, by Policy (Policies) false false R25.htm 024 - Disclosure - Note 3 - Summary of Significant Accounting Policies (Tables) Sheet http://na/role/NoteTables Note 3 - Summary of Significant Accounting Policies (Tables) false false R26.htm 025 - Disclosure - Note 5 - Agency Securities, Available for Sale (Tables) Sheet http://na/role/NoteTables0 Note 5 - Agency Securities, Available for Sale (Tables) false false R27.htm 026 - Disclosure - Note 7 - Fair Value of Financial Instruments (Tables) Sheet http://na/role/NoteTables00 Note 7 - Fair Value of Financial Instruments (Tables) false false R28.htm 027 - Disclosure - Note 8 - Repurchase Agreements (Tables) Sheet http://na/role/NoteTables000 Note 8 - Repurchase Agreements (Tables) false false R29.htm 028 - Disclosure - Note 9 - Derivatives (Tables) Sheet http://na/role/NoteTables0000 Note 9 - Derivatives (Tables) false false R30.htm 029 - Disclosure - Note 11 - Stockholders' Equity (Tables) Sheet http://na/role/NoteTables00000 Note 11 - Stockholders' Equity (Tables) false false R31.htm 030 - Disclosure - Note 13 - Income Taxes (Tables) Sheet http://na/role/NoteTables000000 Note 13 - Income Taxes (Tables) false false R32.htm 031 - Disclosure - Note 2 - Organization and Nature of Business Operations (Detail) Sheet http://na/role/NoteDetail Note 2 - Organization and Nature of Business Operations (Detail) false false R33.htm 032 - Disclosure - Note 3 - Summary of Significant Accounting Policies (Detail) Sheet http://na/role/NoteDetail0 Note 3 - Summary of Significant Accounting Policies (Detail) false false R34.htm 033 - Disclosure - Note 3 - Summary of Significant Accounting Policies (Detail) - Net Margin Collateral Posted (Held) Sheet http://na/role/NetMarginCollateralPostedHeldTable Note 3 - Summary of Significant Accounting Policies (Detail) - Net Margin Collateral Posted (Held) false false R35.htm 035 - Disclosure - Note 5 - Agency Securities, Available for Sale (Detail) Sheet http://na/role/NoteDetail000 Note 5 - Agency Securities, Available for Sale (Detail) false false R36.htm 036 - Disclosure - Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Agency Securities Sheet http://na/role/UnrealizedGainorLossPositionandComponentsofCarryingValueofAvailableforSaleAgencySecuritiesTable Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Agency Securities false false R37.htm 037 - Disclosure - Note 5 - Agency Securities, Available for Sale (Detail) - Summary of Weighted Average Lives of Agency Securities Sheet http://na/role/SummaryofWeightedAverageLivesofAgencySecuritiesTable Note 5 - Agency Securities, Available for Sale (Detail) - Summary of Weighted Average Lives of Agency Securities false false R38.htm 038 - Disclosure - Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Losses and Estimated Fair Value of Agency Securities Sheet http://na/role/UnrealizedLossesandEstimatedFairValueofAgencySecuritiesTable Note 5 - Agency Securities, Available for Sale (Detail) - Unrealized Losses and Estimated Fair Value of Agency Securities false false R39.htm 039 - Disclosure - Note 6 - Non-Agency Securities, Trading (Detail) - Non-Agency Securities Sheet http://na/role/NonAgencySecuritiesTable Note 6 - Non-Agency Securities, Trading (Detail) - Non-Agency Securities false false R40.htm 040 - Disclosure - Note 6 - Non-Agency Securities, Trading (Detail) - Summary of Weighted Average Lives of Agency Securities Sheet http://na/role/SummaryofWeightedAverageLivesofAgencySecuritiesTable0 Note 6 - Non-Agency Securities, Trading (Detail) - Summary of Weighted Average Lives of Agency Securities false false R41.htm 041 - Disclosure - Note 7 - Fair Value of Financial Instruments (Detail) Sheet http://na/role/NoteDetail0000 Note 7 - Fair Value of Financial Instruments (Detail) false false R42.htm 042 - Disclosure - Note 7 - Fair Value of Financial Instruments (Detail) - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis Sheet http://na/role/SummaryofAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisTable Note 7 - Fair Value of Financial Instruments (Detail) - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis false false R43.htm 043 - Disclosure - Note 7 - Fair Value of Financial Instruments (Detail) - Carrying Values and Fair Values of Financial Assets and Liabilities Sheet http://na/role/CarryingValuesandFairValuesofFinancialAssetsandLiabilitiesTable Note 7 - Fair Value of Financial Instruments (Detail) - Carrying Values and Fair Values of Financial Assets and Liabilities false false R44.htm 044 - Disclosure - Note 7 - Fair Value of Financial Instruments (Detail) - Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis Sheet http://na/role/ChangesinLevel3AssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisTable Note 7 - Fair Value of Financial Instruments (Detail) - Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis false false R45.htm 045 - Disclosure - Note 7 - Fair Value of Financial Instruments (Detail) - Range of Estimates of Cumulative Default and Loss Severities and Discount Rates Sheet http://na/role/RangeofEstimatesofCumulativeDefaultandLossSeveritiesandDiscountRatesTable Note 7 - Fair Value of Financial Instruments (Detail) - Range of Estimates of Cumulative Default and Loss Severities and Discount Rates false false R46.htm 046 - Disclosure - Note 8 - Repurchase Agreements (Detail) Sheet http://na/role/NoteDetail00000 Note 8 - Repurchase Agreements (Detail) false false R47.htm 047 - Disclosure - Note 8 - Repurchase Agreements (Detail) - Repurchase Agreements Information Sheet http://na/role/RepurchaseAgreementsInformationTable Note 8 - Repurchase Agreements (Detail) - Repurchase Agreements Information false false R48.htm 048 - Disclosure - Note 8 - Repurchase Agreements (Detail) - Repurchase Agreements Information - Additional Sheet http://na/role/RepurchaseAgreementsInformationAdditionalTable Note 8 - Repurchase Agreements (Detail) - Repurchase Agreements Information - Additional false false R49.htm 050 - Disclosure - Note 9 - Derivatives (Detail) - Derivatives Information Sheet http://na/role/DerivativesInformationTable Note 9 - Derivatives (Detail) - Derivatives Information false false R50.htm 051 - Disclosure - Note 9 - Derivatives (Detail) - Derivatives Information - Additional Sheet http://na/role/DerivativesInformationAdditionalTable Note 9 - Derivatives (Detail) - Derivatives Information - Additional false false R51.htm 052 - Disclosure - Note 9 - Derivatives (Detail) - Location and Information of Derivatives Sheet http://na/role/LocationandInformationofDerivativesTable Note 9 - Derivatives (Detail) - Location and Information of Derivatives false false R52.htm 053 - Disclosure - Note 10 - Share-Based Compensation (Detail) Sheet http://na/role/NoteDetail0000000 Note 10 - Share-Based Compensation (Detail) false false R53.htm 054 - Disclosure - Note 11 - Stockholders' Equity (Detail) - Common Stock Dividend Transactions Sheet http://na/role/CommonStockDividendTransactionsTable Note 11 - Stockholders' Equity (Detail) - Common Stock Dividend Transactions false false R54.htm 055 - Disclosure - Note 12 - Net Income per Common Share (Detail) Sheet http://na/role/NoteDetail00000000 Note 12 - Net Income per Common Share (Detail) false false R55.htm 056 - Disclosure - Note 13 - Income Taxes (Detail) Sheet http://na/role/NoteDetail000000000 Note 13 - Income Taxes (Detail) false false R56.htm 057 - Disclosure - Note 13 - Income Taxes (Detail) - Reconciliation of GAAP Net Income to Estimated REIT Taxable Income Sheet http://na/role/ReconciliationofGAAPNetIncometoEstimatedREITTaxableIncomeTable Note 13 - Income Taxes (Detail) - Reconciliation of GAAP Net Income to Estimated REIT Taxable Income false false R57.htm 058 - Disclosure - Note 14 - Commitments and Contingencies (Detail) Sheet http://na/role/NoteDetail0000000000 Note 14 - Commitments and Contingencies (Detail) false false R58.htm 059 - Disclosure - Note 15 - Related Party Transactions (Detail) Sheet http://na/role/NoteDetail00000000000 Note 15 - Related Party Transactions (Detail) false false R59.htm 060 - Disclosure - Note 17 - Subsequent events (Detail) Sheet http://na/role/NoteDetail000000000000 Note 17 - Subsequent events (Detail) false false All Reports Book All Reports Element jmi_HaircutForRepurchaseAgreements had a mix of decimals attribute values: 3 4. Element us-gaap_CommonStockSharesOutstanding had a mix of decimals attribute values: -3 0. Element us-gaap_PaymentsOfDividendsCommonStock had a mix of decimals attribute values: -5 -3. 'Monetary' elements on report '056 - Disclosure - Note 13 - Income Taxes (Detail)' had a mix of different decimal attribute values. Process Flow-Through: 001 - Statement - Condensed Balance Sheets (Unaudited) Process Flow-Through: 002 - Statement - Condensed Balance Sheets (Unaudited) (Parentheticals) Process Flow-Through: Removing column 'Sep. 24, 2012' Process Flow-Through: Removing column 'Jun. 18, 2012' Process Flow-Through: 003 - Statement - Condensed Statement of Operations (Unaudited) Process Flow-Through: Removing column '1 Months Ended Mar. 31, 2013' Process Flow-Through: Removing column '1 Months Ended Feb. 28, 2013' Process Flow-Through: Removing column '1 Months Ended Jan. 31, 2013' Process Flow-Through: 004 - Statement - Condensed Statement of Comprehensive Income (Unaudited) Process Flow-Through: 006 - Statement - Condensed Statement of Cash Flows (Unaudited) jmi-20130331.xml jmi-20130331.xsd jmi-20130331_cal.xml jmi-20130331_def.xml jmi-20130331_lab.xml jmi-20130331_pre.xml true true