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Income Taxes - Reconciliation of Differences Between Federal Statutory and Effective Income Tax Rate (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 28, 2014
Dec. 29, 2013
Dec. 30, 2012
Income Tax Disclosure [Abstract]      
Computed "expected" tax expense $ 2,411us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 380us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate $ 2,726us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate
Permanent differences 97pbpb_IncomeTaxReconciliationPermanentDifference 63pbpb_IncomeTaxReconciliationPermanentDifference  
State and local income taxes, net of federal income tax effect 460us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 145us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes 358us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes
FICA and other tax credits (222)us-gaap_IncomeTaxReconciliationTaxCredits (113)us-gaap_IncomeTaxReconciliationTaxCredits (41)us-gaap_IncomeTaxReconciliationTaxCredits
Change in valuation allowance     (19,078)us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance
Non-deductible IPO costs   195us-gaap_IncomeTaxReconciliationNondeductibleExpense  
Rate change and true-ups 2us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate (874)us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate 41us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate
Income tax expense (benefit) $ 2,748us-gaap_IncomeTaxExpenseBenefit $ (204)us-gaap_IncomeTaxExpenseBenefit $ (15,994)us-gaap_IncomeTaxExpenseBenefit