Represents the remaining term under an operating lease agreement.

No definition available.

Name:	cosi_OperatingLeasesRemainingLeaseTerm
Namespace Prefix:	cosi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation maturing in the next fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the deferred credit for an incentive or inducement received by a lessee from a lessor, in order to motivate the lessee to enter the lease agreement, which incentive or inducement is to be recognized as a reduction of rental expense over the lease term.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e40010-112707

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Lease Incentive

-URI http://asc.fasb.org/extlink&oid=6516590

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 55

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6584307&loc=d3e41620-112719

+ Details

Name:	us-gaap_IncentiveFromLessor
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Term of the lessee's leasing arrangement renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_LesseeLeasingArrangementsOperatingLeasesRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_OperatingLeasedAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the payments that the lessee is obligated to make or can be required to make in connection with a property under the terms of an agreement classified as an operating lease, excluding contingent rentals and a guarantee by the lessee of the lessor's debt and the lessee's obligation to pay (apart from the rental payments) executory costs such as insurance, maintenance, and taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 25

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=7661868&loc=d3e34039-112682

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseMinimumRentals
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Commitments and Contingencies 2 (Details) (Restaurant leaseholds [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 29, 2014	Dec. 30, 2013	Dec. 31, 2012
Commitments and contingencies [Line Items]
Contractual obligation	1.1us-gaap_ContractualObligation	$ 1.7us-gaap_ContractualObligation	$ 2.1us-gaap_ContractualObligation
Landlord allowances presented as a long-term liability in other liabilities	0.1us-gaap_IncentiveFromLessor	0.2us-gaap_IncentiveFromLessor	0.5us-gaap_IncentiveFromLessor
Minimum [Member]
Commitments and contingencies [Line Items]
Renewal option, period	3 years
Maximum [Member]
Commitments and contingencies [Line Items]
Renewal option, period	5 years
Terminated operating leases [Member]
Commitments and contingencies [Line Items]
Contractual obligation	0.2
Future minimum lease payments	0.3
Contractual obligation, current	0.1
Terminated operating leases [Member] \| Minimum [Member]
Commitments and contingencies [Line Items]
Operating lease, remaining term	1 year
Terminated operating leases [Member] \| Maximum [Member]
Commitments and contingencies [Line Items]
Operating lease, remaining term	3 years
Standby letters of credit [Member]
Commitments and contingencies [Line Items]
Letters of credit provided as security deposits	0.4