| Document and Entity Information | Dec. 22, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001055160 |
| Document Type | 8-K |
| Document Period End Date | Dec. 22, 2020 |
| Entity Registrant Name | MFA FINANCIAL, INC. |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 1-13991 |
| Entity Tax Identification Number | 13-3974868 |
| Entity Address, Address Line One | 350 Park Avenue |
| Entity Address, Address Line Two | 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 |
| 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 And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | MFA |
| Security Exchange Name | NYSE |
| M 7.50 Series B Cumulative Redeemable Preferred Stock Par Value 0.01 Per Share 2 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 7.50% Series B Cumulative Redeemable Preferred Stock, par value $0.01 per share |
| Trading Symbol | MFA/PB |
| Security Exchange Name | NYSE |
| M 6.50 Series C Fixed To Floating Rate Cumulative Redeemable Preferred Stock Par Value 0.01 Per Share 1 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 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 |
| Senior Note Due 2042 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 8.00% Senior Notes due 2042 |
| Trading Symbol | MFO |
| Security Exchange Name | NYSE |
