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Note 15 - Quarterly Financial Information (unaudited) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
0 Months Ended
Oct. 27, 2014
Nov. 21, 2014
Oct. 27, 2014
Note 15 - Quarterly Financial Information (unaudited) (Details) [Line Items]      
Preferred Stock, Accretion of Redemption Discount (in Dollars) $ 1.3us-gaap_PreferredStockAccretionOfRedemptionDiscount    
Stock Issued During Period Shares Warrants Exercised 498,889prto_StockIssuedDuringPeriodSharesWarrantsExercised    
IPO [Member]      
Note 15 - Quarterly Financial Information (unaudited) (Details) [Line Items]      
Proceeds from Issuance Initial Public Offering (in Dollars) 62.5us-gaap_ProceedsFromIssuanceInitialPublicOffering
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
   
Stock Issued During Period, Shares, New Issues 7,026,500us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
   
Class of Warrant or Right, Number of Securities Called by Warrants or Rights 916,500us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
916,500us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
916,500us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
Conversion of Stock, Shares Issued 8,651,805us-gaap_ConversionOfStockSharesIssued1
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember
   
Warrant [Member]      
Note 15 - Quarterly Financial Information (unaudited) (Details) [Line Items]      
Proceeds from Issuance or Sale of Equity (in Dollars) $ 1.4us-gaap_ProceedsFromIssuanceOrSaleOfEquity
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_WarrantMember