Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2015	Jun. 30, 2014	Jun. 29, 2015	Jun. 30, 2014
Net Loss Per Share [Abstract]
Net loss attributable to Cosi, Inc.	$ (3,874)	$ (4,814)	$ (8,188)	$ (7,940)
Net loss per share attributable to Cosi, Inc. [Abstract]
Basic and diluted (in dollars per share)	$ (0.08)	$ (0.27)	$ (0.20)	$ (0.44)
Basic and diluted loss per share [Abstract]
Weighted average number of shares outstanding (in shares)	45,726,432	18,148,966	41,522,803	18,101,773
Restricted shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the computation of basic and diluted earnings per share (in shares)	1,327,463	1,082,539	1,327,463	1,082,539
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the computation of basic and diluted earnings per share (in shares)				1,650,000
Out-of-the-Money Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the computation of basic and diluted earnings per share (in shares)	2,500	7,500	2,500	7,500