Residential Whole Loans (Fair Value Components of Net Income) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Receivables [Abstract]
Net unrealized (losses)/gains	$ (287,935)	$ 32,088
Other Income	(440)	(598)
Total	$ (288,375)	$ 31,490

Residential Whole Loans, Fair Value, Net Income (Loss), Coupon Payments, Realized Gains, and Other Income Received

No definition available.

Name:	mfa_ResidentialWholeLoansFairValueNetIncomeLossCouponPaymentsRealizedGainsAndOtherIncomeReceived
Namespace Prefix:	mfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration