Cover page - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2019
Entity File Number	1-13991
Entity Registrant Name	MFA FINANCIAL, INC.
Entity Central Index Key	0001055160
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	13-3974868
Entity Address, Address Line One	350 Park Avenue, 20th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10022
City Area Code	212
Local Phone Number	207-6400
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		451,770,207
Common Stock, par value $0.01 per share
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	MFA
Security Exchange Name	NYSE
7.50% Series B Cumulative Redeemable Preferred Stock, par value $0.01 per share
Entity Information [Line Items]
Title of 12(b) Security	7.50% Series B Cumulative RedeemablePreferred Stock, par value $0.01 per share
Trading Symbol	MFA/PB
Security Exchange Name	NYSE
8.00% Senior Notes due 2042
Entity Information [Line Items]
Title of 12(b) Security	8.00% Senior Notes due 2042
Trading Symbol	MFO
Security Exchange Name	NYSE