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Residential Whole Loans (Narrative) (Details) - USD ($) $ in Billions | Sep. 30, 2019 | Dec. 31, 2018
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Receivables [Abstract] |  |
Total residential whole loans | $ 6.4 | $ 4.7

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- Definition Loans, Including Fair Value Loans, Credit Impaired Loans and Other Loans at Carrying Value + References No definition available. + Details
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Namespace Prefix: | mfa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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