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Note 2 - Summary of Significant Accounting Policies (Details) (USD $)
0 Months Ended 3 Months Ended 12 Months Ended 0 Months Ended
Oct. 27, 2014
Sep. 30, 2014
Dec. 31, 2014
May 13, 2014
Dec. 31, 2013
Dec. 31, 2012
Nov. 21, 2014
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]              
Payments of Stock Issuance Costs     $ 452,000us-gaap_PaymentsOfStockIssuanceCosts        
Conversion of Stock, Shares Converted (in Shares) 8,651,805us-gaap_ConversionOfStockSharesConverted1            
Number of Operating Segments     1us-gaap_NumberOfOperatingSegments        
Number of Reportable Segments     1us-gaap_NumberOfReportableSegments        
Deferred Finance Costs, Gross     18,000us-gaap_DeferredFinanceCostsGross   18,000us-gaap_DeferredFinanceCostsGross 0us-gaap_DeferredFinanceCostsGross  
Revenues   2,948,000us-gaap_Revenues 2,948,000us-gaap_Revenues        
Series D Preferred Stock [Member] | First Tranche [Member]              
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]              
Payments of Stock Issuance Costs     400,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesDPreferredStockMember
/ us-gaap_StatementScenarioAxis
= prto_FirstTrancheMember
       
Series D Preferred Stock [Member] | Second and Third Tranches [Member]              
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]              
Payments of Stock Issuance Costs     100,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesDPreferredStockMember
/ us-gaap_StatementScenarioAxis
= prto_SecondAndThirdTranchesMember
       
Series D Preferred Stock [Member]              
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]              
Share Price (in Dollars per share)       $ 0.588656us-gaap_SharePrice
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesDPreferredStockMember
     
Payments of Stock Issuance Costs     500,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesDPreferredStockMember
500,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_StatementClassOfStockAxis
= us-gaap_SeriesDPreferredStockMember
     
IPO [Member]              
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]              
Stock Issued During Period, Shares, New Issues (in Shares) 7,026,500us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
           
Share Price (in Dollars per share) 10.00us-gaap_SharePrice
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
           
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in Shares) 916,500us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
          916,500us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
Proceeds from Issuance Initial Public Offering 62,500,000us-gaap_ProceedsFromIssuanceInitialPublicOffering
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
           
Payments of Stock Issuance Costs 7,800,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
           
Conversion of Stock, Shares Converted (in Shares) 8,651,805us-gaap_ConversionOfStockSharesConverted1
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember