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v3.20.4

Commitments and Contingencies (Representations and Warranties in Connection with Loan Securitization Transactions) (Details) | Dec. 31, 2020 USD ($)
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Commitments and Contingencies Disclosure [Abstract] |
Allowance for repurchased loans | $ 0

X
- Definition Repurchase Loans, Allowance + References No definition available. + Details
Name: | mfa_RepurchaseLoansAllowance
Namespace Prefix: | mfa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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