Document and Entity Information Document and Entity Information - $ / shares	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Jul. 30, 2021	Dec. 31, 2020
Document Information [Line Items]
Document Type		10-Q
Document Quarterly Report		true
Document Period End Date	Jun. 30, 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			34,591,535
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 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 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