Cover - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-13792
Entity Registrant Name	Systemax Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	11-3262067
Entity Address, Address Line One	11 Harbor Park Drive
Entity Address, City or Town	Port Washington
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	11050
City Area Code	516
Local Phone Number	608-7000
Title of 12(b) Security	Common Stock ($.01 par value)
Trading Symbol	SYX
Security Exchange Name	NYSE
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		37,719,099
Entity Central Index Key	0000945114
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false