Document and Entity Information Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 25, 2021	Jun. 30, 2020	Dec. 31, 2019
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2020
Entity File Number	1-9819
Entity Registrant Name	DYNEX CAPITAL, INC.
Entity Central Index Key	0000826675
Entity Incorporation, State or Country Code	VA
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 315,650,564
Entity Common Stock, Shares Outstanding		26,860,470
Common Stock, Par or Stated Value Per Share	$ 0.01			$ 0.01
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
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
Trading Symbol	N/A
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