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Organization and Summary of Significant Accounting Policies (Details)
12 Months Ended
Dec. 29, 2014
Week
State
Dec. 30, 2013
Week
Dec. 31, 2012
Week
Organization [Line Items]      
Number of states in which the entity owns and operates restaurants 16us-gaap_NumberOfStatesInWhichEntityOperates    
Fiscal Year [Abstract]      
Number of weeks in a fiscal year 52cosi_LengthOfFiscalYear 52cosi_LengthOfFiscalYear 52cosi_LengthOfFiscalYear
Company-owned [Member]      
Organization [Line Items]      
Number of company-owned restaurants 64us-gaap_NumberOfRestaurants
/ us-gaap_FranchisorDisclosureAxis
= us-gaap_EntityOperatedUnitsMember
   
Franchises [Member]      
Organization [Line Items]      
Number of company-owned restaurants 47us-gaap_NumberOfRestaurants
/ us-gaap_FranchisorDisclosureAxis
= us-gaap_FranchisedUnitsMember