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REVENUE - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 25, 2020
Disaggregation of Revenue [Line Items]    
Revenue from contract with customer $ 155,282 $ 143,170
Shack Sales [Member]    
Disaggregation of Revenue [Line Items]    
Revenue from contract with customer 150,668 138,048
Sales-Based Royalties [Member]    
Disaggregation of Revenue [Line Items]    
Revenue from contract with customer 4,425 4,944
Initial territory and opening fees    
Disaggregation of Revenue [Line Items]    
Revenue from contract with customer $ 189 $ 178