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Stock Based Compensation - Additional Information (Detail) (USD $)
1 Months Ended 12 Months Ended 0 Months Ended
Aug. 31, 2013
Dec. 28, 2014
Dec. 29, 2013
Dec. 30, 2012
Oct. 09, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Non-voting Common stock conversion basis ratio   1pbpb_CommonStockConversionBasisRatio      
Weighted average share value of unrestricted common stock $ 100,000us-gaap_AllocatedShareBasedCompensationExpense   $ 10,000,000us-gaap_AllocatedShareBasedCompensationExpense    
Recognized stock-based compensation expense   2,543,000us-gaap_ShareBasedCompensation 11,610,000us-gaap_ShareBasedCompensation 2,825,000us-gaap_ShareBasedCompensation  
Unrecognized stock compensation expense   5,500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions 5,500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions 1,600,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions  
Unrecognized stock compensation expense, recognition period   Through 2018      
Unrestricted Common Stock Granted [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Recognized stock-based compensation expense   400,000us-gaap_ShareBasedCompensation
/ us-gaap_AwardTypeAxis
= pbpb_UnrestrictedCommonsSharesMember
     
IPO [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Issuance of unrestricted common stock         8,625,000us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
Recognized stock-based compensation expense     7,600,000us-gaap_ShareBasedCompensation
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
   
Non-Employee Board Of Directors [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Issuance of unrestricted common stock   28,240us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_TitleOfIndividualAxis
= pbpb_NonEmployeeBoardOfDirectorsMember
     
Weighted average grant-date share price   $ 15.29us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
/ us-gaap_TitleOfIndividualAxis
= pbpb_NonEmployeeBoardOfDirectorsMember
     
Weighted average share value of unrestricted common stock   $ 400,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_TitleOfIndividualAxis
= pbpb_NonEmployeeBoardOfDirectorsMember
     
2001 Equity Incentive Plans [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock reserved for issuance   746,749us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= pbpb_TwoThousandOnePlanMember
     
2001 Equity Incentive Plans [Member] | Non-Voting Common Stock [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock issued to key executive   500,000pbpb_CommonStockOptionsGrantedShares
/ us-gaap_PlanNameAxis
= pbpb_TwoThousandOnePlanMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_NonvotingCommonStockMember
     
2013 Long-Term Incentive Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock reserved for issuance   840,437us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= pbpb_LongTermIncentivePlanTwoThousandThirteenMember
     
Options granted   712,767pbpb_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsCumulativeNumber
/ us-gaap_PlanNameAxis
= pbpb_LongTermIncentivePlanTwoThousandThirteenMember
     
2001 and 2004 Equity Incentive Plans and 2013 Long-Term Incentive Plan [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Exercise price of options outstanding, lower limit   $ 7.00us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
/ us-gaap_PlanNameAxis
= pbpb_TwoThousandOneAndTwoThousandFourEquityIncentivePlansAndTwoThousandThirteenLongTermIncentivePlanMember
     
Exercise price of options outstanding, higher limit   $ 20.53us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
/ us-gaap_PlanNameAxis
= pbpb_TwoThousandOneAndTwoThousandFourEquityIncentivePlansAndTwoThousandThirteenLongTermIncentivePlanMember
     
2001 and 2004 Equity Incentive Plans and 2013 Long-Term Incentive Plan [Member] | Maximum [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Exercisable period from the date of grant   10 years      
Options issued and outstanding, last expiration date   Dec. 31, 2024      
Options vesting period   5 years