REVENUE Contract Balances (Details) - USD ($) $ in Thousands	Dec. 30, 2020	Dec. 25, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Gift card liability	$ 2,637	$ 2,258
Deferred revenue, current	608	511
Deferred revenue, long-term	12,151	11,310
Shack sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, asset, net	5,373	4,265
Licensing receivables, net of allowance for doubtful accounts
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, asset, net	$ 2,647	$ 4,510

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130533-203044

Name:	us-gaap_ContractWithCustomerAssetNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant