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Residential Whole Loans (Narrative) (Details) - USD ($) $ in Billions	Sep. 30, 2019	Dec. 31, 2018
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

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