Name:	mfa_RepurchaseAgreementCounterpartyRiskAsPercentageOfStockholdersEquity
Namespace Prefix:	mfa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the minimum percentage of stockholders' equity at risk with respect to repurchase agreements with any single counterparty.

No definition available.

Name:	mfa_RepurchaseAgreementCounterpartyRiskMinimumAsPercentageOfStockholdersEquity
Namespace Prefix:	mfa_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the number of parties with whom the entity had repurchase agreements on the balance sheet date.

No definition available.

Name:	mfa_RepurchaseAgreementsNumberOfCounterparties
Namespace Prefix:	mfa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The amount at risk under repurchase agreements is defined as the excess of carrying amount (or market value, if higher than the carrying amount or if there is no carrying amount) of the securities or other assets sold under agreement to repurchase, including accrued interest plus any cash or other assets on deposit to secure the repurchase obligation, over the amount of the repurchase liability (adjusted for accrued interest).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(B)(iii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_RepurchaseAgreementCounterpartyAmountAtRisk
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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.

No definition available.

Name:	us-gaap_RepurchaseAgreementCounterpartyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Weighted average maturity (weighted by amount of the agreement) of repurchase agreements with the counterparty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Data Type:	xbrli:durationItemType
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Period Type:	duration

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Name:	us-gaap_CounterpartyNameAxis=mfa_WellsFargoMember
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Name:	us-gaap_CounterpartyNameAxis=mfa_WellsFargoBankMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=mfa_WellsFargoSecuritiesLlcMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=mfa_CreditSuisseMember
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Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=mfa_CreditSuisseAGMember
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Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=mfa_CreditSuisse2Member
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Data Type:	na
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Name:	us-gaap_CounterpartyNameAxis=mfa_RBCMember
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Name:	us-gaap_CounterpartyNameAxis=mfa_RBCBarbadosMember
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Name:	us-gaap_CounterpartyNameAxis=mfa_RoyalBankofCanadaMember
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