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Commitments and Contingencies (Residential Whole Loan Purchase Commitments) (Details) $ in Millions | Mar. 31, 2021 USD ($)
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Other Commitments [Line Items] |
Unsettled residential whole loans | $ 112.2
Residential whole loans |
Other Commitments [Line Items] |
Unsettled residential whole loans | $ 112.2

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- Definition Unsettled Residential Whole Loans + References No definition available. + Details
Name: | mfa_UnsettledResidentialWholeLoans
Namespace Prefix: | mfa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_OtherCommitmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FinancialInstrumentAxis=mfa_ResidentialWholeLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |