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Earnings Per Share - Schedule of the Calculation of Weighted Average Shares Outstanding for Basic and Diluted Earnings per Share (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Sep. 25, 2016
Sep. 27, 2015
Sep. 25, 2016
Sep. 27, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]        
Net income attributable to Potbelly Corporation $ 1,795 $ 1,401 $ 6,256 $ 4,393
Weighted average common shares outstanding-basic 25,240,374 27,850,394 25,772,846 28,450,063
Plus: Effect of potential stock options exercise 533,249 471,579 514,257 630,043
Plus: Effect of potential warrant exercise 56,347 47,802 54,810 57,431
Weighted average common shares outstanding-diluted 25,829,970 28,369,775 26,341,913 29,137,537
Income per share available to common stockholders-basic $ 0.07 $ 0.05 $ 0.24 $ 0.15
Income per share available to common stockholders-diluted $ 0.07 $ 0.05 $ 0.24 $ 0.15
Common Share Options [Member]        
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]        
Potentially dilutive shares that are considered anti-dilutive 1,233,294 1,192,579 1,236,599 803,582
Warrants [Member]        
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]        
Potentially dilutive shares that are considered anti-dilutive 0 0 0 0