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Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Financial Data (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 12 Months Ended
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Aug. 31, 2013 | Dec. 29, 2013
Quarterly Financial Information Disclosure [Abstract] |  |
One-time costs associated with IPO |  | $ 10.6 pbpb_InitialPublicOfferingCost
One-time charges for stock compensation | $ 0.1 us-gaap_AllocatedShareBasedCompensationExpense | $ 10.0 us-gaap_AllocatedShareBasedCompensationExpense

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- Definition Initial Public Offering Cost + References No definition available. + Details
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Namespace Prefix: | pbpb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
Name: | us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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