Document and Entity Information Document and Entity Information - $ / shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021	Dec. 31, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-9819
Entity Registrant Name	DYNEX CAPITAL, INC.
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	52-1549373
Entity Address, Address Line One	4991 Lake Brook Drive
Entity Address, Address Line Two	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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		30,879,569
Common Stock, Par or Stated Value Per Share	$ 0.01		$ 0.01
Entity Central Index Key	0000826675
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
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 B Preferred Stock
Document Information [Line Items]
Title of 12(b) Security	7.625% Series B Cumulative Redeemable Preferred Stock, par value $0.01 per share
Series C Preferred Stock
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