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Commitments and Contingencies (Corporate Loans) (Details) - Corporate Loans $ in Millions	Dec. 31, 2019 USD ($)
Other Commitments [Line Items]
Commitment to lend	$ 150.0
Amount drawn	$ 109.5

X

- Definition

Financing Receivable, Amount Drawn

+ References

No definition available.

+ Details

Name:	mfa_FinancingReceivableAmountDrawn
Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Financing Receivable, Commitment to Lend

+ References

No definition available.

+ Details

Name:	mfa_FinancingReceivableCommitmenttoLend
Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- 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

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=mfa_CorporateLoans2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: