Summary of Significant Accounting Policies - Financing Agreements (Details)	12 Months Ended
Dec. 31, 2021
Accounting Policies [Abstract]
Repurchase financing period, low end of range	1 month
Repurchase financing period, high end of range	6 months
Repurchase Agreements Financing Collateralized, Period, High End of Range	12 months

Represents the high end of the range of the typical period for repurchase financing agreements.

No definition available.

Name:	mfa_RepurchaseAgreementsFinancingPeriodHighEndOfRange
Namespace Prefix:	mfa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration