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Fair Value of Financial Instruments - Assets Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Sep. 30, 2021
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Fair Value Disclosures [Abstract] |  |
Other real estate, fair value | $ 61.9 | $ 50.0

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- Definition Other Real Estate, Fair 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
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration