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Stock-Based Compensation, Narrative (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum number of shares authorized under plan 5,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized    
Total intrinsic value $ 139,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1    
Weighted average grant date fair value of shares granted (in dollars per share) $ 18.56us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue [1]    
Stock compensation 13,400,000us-gaap_AllocatedShareBasedCompensationExpense 11,100,000us-gaap_AllocatedShareBasedCompensationExpense 9,600,000us-gaap_AllocatedShareBasedCompensationExpense
Stock-based compensation cost recognized, retirement savings plan contributions 2,000,000us-gaap_PensionAndOtherPostretirementBenefitExpense 1,700,000us-gaap_PensionAndOtherPostretirementBenefitExpense 1,400,000us-gaap_PensionAndOtherPostretirementBenefitExpense
Associated current and future income tax benefit recognized 4,100,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 3,600,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 3,200,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Unrecognized compensation cost related to non-vested share-based awards 17,200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized    
Unrecognized compensation cost, weighted-average period for recognition 2 years    
Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum fair value of common stock under ESPP 25,000prft_MaximumFairValueOfCommonStock
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= us-gaap_EmployeeStockMember		    
Annual participation limit 12,500prft_AnnualParticipationLimit
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= us-gaap_EmployeeStockMember		    
Shares purchased under the ESPP (in shares) 15,200us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= us-gaap_EmployeeStockMember		    
ESPP purchase price, percentage of fair market value (in hundredths) 95.00%prft_EsppPurchasePricePercentageOfFairMarketValue
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= us-gaap_EmployeeStockMember		    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum contractual term of stock options 10 years    
Total intrinsic value   1,000,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		 400,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average grant date fair value of shares granted (in dollars per share)   $ 14.62us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 $ 11.31us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Fair value of shares vested $ 15,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 $ 13,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 $ 9,700,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Restricted Stock [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Requisite service period 3 years    
Restricted Stock [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Requisite service period 5 years    
[1] The weighted average grant date fair value of shares granted during 2013 and 2012 was $14.62 and $11.31, respectively.