Document and Entity Information	3 Months Ended
	Mar. 30, 2015	May 07, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	COSI INC
Entity Central Index Key	0001171014
Current Fiscal Year End Date	--12-29
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		47,267,684
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 30, 2015