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Note 12 - 401(k) Savings Plan (Details)
12 Months Ended
Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]  
Defined Contribution Plan, Elective Minimum Annual Contributions Per Employee, Percent 1.00%prto_DefinedContributionPlanElectiveMinimumAnnualContributionsPerEmployeePercent
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay 3.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent