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Accrued Expenses - Summary of Accrued Contract Termination Costs (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 27, 2020 | Dec. 29, 2019
Accrued Liabilities And Other Liabilities [Abstract] |  |
Accrued contract termination costs—beginning balance |  | $ 392
Contract termination costs incurred | $ 3,231 | 3,449
Contract termination costs settled and paid | $ (3,231) | $ (3,841)

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- Definition Contract Termination Costs + References No definition available. + Details
Name: | pbpb_ContractTerminationCosts
Namespace Prefix: | pbpb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Contract Termination Costs Incurred + References No definition available. + Details
Name: | pbpb_ContractTerminationCostsIncurred
Namespace Prefix: | pbpb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Contract Termination Costs Settled And Paid + References No definition available. + Details
Name: | pbpb_ContractTerminationCostsSettledAndPaid
Namespace Prefix: | pbpb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_AccruedLiabilitiesAndOtherLiabilitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration