| Cover | Jul. 28, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 28, 2021 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Registrant Name | DYNEX CAPITAL, INC. |
| Entity Incorporation, State or Country Code | VA |
| Entity File Number | 1-9819 |
| Entity Tax Identification Number | 52-1549373 |
| Entity Address, Address Line One | 4991 Lake Brook Drive, Suite 100 |
| Entity Address, Address Line Two | 4991 Lake Brook Drive, Suite 100 |
| Entity Address, City or Town | Glen Allen, |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 23060-9245 |
| City Area Code | (804) |
| Local Phone Number | 217-5800 |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000826675 |
| Amendment Flag | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | DX |
| Security Exchange Name | NYSE |
| Series C Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 6.900% Series C Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock, par value $0.01 per share |
| Trading Symbol | DXPRC |
| Security Exchange Name | NYSE |
