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Organization and Other Matters - Additional Information (Detail)
$ in Thousands
1 Months Ended 12 Months Ended
Jul. 17, 2020
USD ($)
Dec. 27, 2020
USD ($)
Shop
Dec. 29, 2019
USD ($)
Dec. 30, 2018
USD ($)
Aug. 10, 2020
USD ($)
Mar. 17, 2020
USD ($)
Dec. 31, 2017
USD ($)
Nature Of Business And Basis Of Presentation [Line Items]              
Number of shops franchisees operate | Shop   46          
Income tax expense (benefit)   $ (6,536) $ 14,190 $ (2,195)      
Line of credit facility amount borrowed $ 10,000            
Line of credit facility amount borrowed   55,000          
Cash and cash equivalents   11,126 $ 18,806 $ 19,775     $ 25,530
Revolving Credit Facility [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Line of credit facility amount borrowed $ 14,500            
COVID 19 [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Impairment charge   10,300          
Income tax expense (benefit)   6,700          
CARES Act Of 2020 [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Line of credit facility amount borrowed   33,500          
CARES Act Of 2020 [Member] | Revolving Credit Facility [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Line of credit facility amount borrowed           $ 39,800  
Cash and cash equivalents   $ 44,600          
CARES Act Of 2020 [Member] | Harvest Small Business Finance [Member] | Paycheck Protection Program Loan [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Loan amount         $ 10,000    
Minimum [Member]              
Nature Of Business And Basis Of Presentation [Line Items]              
Number of shops Potbelly Corporation owns or operates | Shop   400