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Commitments and Contingencies (Rehabilitation Loan Commitments) (Details) $ in Millions | Dec. 31, 2020 USD ($)
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Commitments and Contingencies Disclosure [Abstract] |
Unfunded commitment for rehabilitation loans | $ 60.6

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- Definition Unfunded Commitment + References No definition available. + Details
Name: | mfa_UnfundedCommitment
Namespace Prefix: | mfa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration