Cover - shares	9 Months Ended
	Sep. 30, 2021	Nov. 11, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31
Entity File Number	001-32698
Entity Registrant Name	MGT CAPITAL INVESTMENTS, INC.
Entity Central Index Key	0001001601
Entity Tax Identification Number	13-4148725
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	150 Fayetteville Street
Entity Address, Address Line Two	Suite 1110
Entity Address, City or Town	Raleigh
Entity Address, State or Province	NC
Entity Address, Postal Zip Code	27601
City Area Code	(914)
Local Phone Number	630-7430
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		590,970,903