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Income Taxes (Narrative) (Details) (USD $)
 12 Months Ended
Jul. 31, 2014
Jul. 31, 2013
Income Tax Disclosure [Line Items]    
Current Income Tax Expense (Benefit) $ 1,600us-gaap_CurrentIncomeTaxExpenseBenefit $ 1,600us-gaap_CurrentIncomeTaxExpenseBenefit
Tax Credit Carryforward, Deferred Tax Asset 17,300,000us-gaap_TaxCreditCarryforwardDeferredTaxAsset  
Valuation Allowance, Deferred Tax Asset, Change in Amount 3,121,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount  
Transaction period 3 years  
Ownership Change Percent Points Of Outstanding Stock 50.00%pure_OwnershipChangePercentPointsOfOutstandingStock  
Accrued interest or penalties 0us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued 0us-gaap_IncomeTaxExaminationPenaltiesAndInterestAccrued
Unrecognized tax benefits 0us-gaap_UnrecognizedTaxBenefits  
Internal Revenue Service (IRS) [Member]    
Income Tax Disclosure [Line Items]    
Operating Loss Carryforwards 83,600,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember		 75,200,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_InternalRevenueServiceIRSMember
Operating Loss Carryforwards, Expiration Dates Jul. 31, 2034  
State and Local Jurisdiction [Member]    
Income Tax Disclosure [Line Items]    
Operating Loss Carryforwards $ 71,800,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember		 $ 64,900,000us-gaap_OperatingLossCarryforwards
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember
Maximum [Member] | State and Local Jurisdiction [Member]    
Income Tax Disclosure [Line Items]    
Operating Loss Carryforwards, Expiration Dates Jul. 31, 2034  
Minimum [Member] | State and Local Jurisdiction [Member]    
Income Tax Disclosure [Line Items]    
Operating Loss Carryforwards, Expiration Dates Jul. 31, 2015