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Operating Leases - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 28, 2014 Option | Dec. 29, 2013 | Dec. 30, 2012
Leases, Operating [Abstract] |  |  |
Initial operating lease period | 10 years |  |
Number of renewal options under operating leases | 2 pbpb_OperatingLeaseNumberOfRenewals |  |
Operating lease rent increment term | 5 years |  |
Operating lease period for expiration or renewal | 2015 to 2029 |  |
Letters of credit in lieu of rent deposits | $ 0.6 us-gaap_LettersOfCreditOutstandingAmount | $ 0.6 us-gaap_LettersOfCreditOutstandingAmount | $ 0.6 us-gaap_LettersOfCreditOutstandingAmount
Letters of credit annual fee percentage | 1.50%pbpb_LetterOfCreditInterestPercentage |  |

X
- Definition Letter Of Credit Interest Percentage + References No definition available. + Details
Name: | pbpb_LetterOfCreditInterestPercentage
Namespace Prefix: | pbpb_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The range of years in which current lease agreements either expire or become subject to renewal clauses. + References No definition available. + Details
Name: | pbpb_OperatingLeaseAgreementExpirationOrRenewalPeriodRange
Namespace Prefix: | pbpb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Operating Lease Number Of Renewals + References No definition available. + Details
Name: | pbpb_OperatingLeaseNumberOfRenewals
Namespace Prefix: | pbpb_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Operating Lease Rent Increment Term + References No definition available. + Details
Name: | pbpb_OperatingLeaseRentIncrementTerm
Namespace Prefix: | pbpb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Operating Leases Initial Contractual Lease Period + References No definition available. + Details
Name: | pbpb_OperatingLeasesInitialContractualLeasePeriod
Namespace Prefix: | pbpb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_LeasesOperatingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant