| Cover | Dec. 15, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 15, 2021 |
| Entity File Number | 1-13991 |
| Entity Registrant Name | MFA FINANCIAL, INC. |
| Entity Central Index Key | 0001055160 |
| Entity Tax Identification Number | 13-3974868 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | One Vanderbilt Avenue |
| Entity Address, Address Line Two | 48th Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10017 |
| City Area Code | 212 |
| Local Phone Number | 207-6400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | MFA |
| Security Exchange Name | NYSE |
| Series B Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 7.50% Series B Cumulative Redeemable Preferred Stock, par value $0.01 per share |
| Trading Symbol | MFA/PB |
| Security Exchange Name | NYSE |
| Series C Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 6.50% Series C Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock, par value $0.01 per share |
| Trading Symbol | MFA/PC |
| Security Exchange Name | NYSE |
