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Capital Stock - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 0 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 31, 2014
Feb. 07, 2014
Dec. 31, 2010
Feb. 29, 2012
Jan. 31, 2012
Sep. 30, 2011
Nov. 30, 2013
Aug. 31, 2014
Mar. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Preferred stock, shares authorized 5,000,000us-gaap_PreferredStockSharesAuthorized 5,000,000us-gaap_PreferredStockSharesAuthorized                    
Preferred stock, shares outstanding 0us-gaap_PreferredStockSharesOutstanding 0us-gaap_PreferredStockSharesOutstanding                    
Preferred stock, shares issued 0us-gaap_PreferredStockSharesIssued 0us-gaap_PreferredStockSharesIssued                    
Reserve of common stock for future issuance 6,585,454us-gaap_CommonStockCapitalSharesReservedForFutureIssuance 5,399,180us-gaap_CommonStockCapitalSharesReservedForFutureIssuance                    
Performance-based restricted stock units granted 1,368,761us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod 577,528us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod                    
Number of stock option outstanding, granted 1,256,559us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross 631,775us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross 698,240us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross                  
Weighted-average grant date fair value $ 19.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 16.48us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 14.54us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue                  
Aggregate grant date fair value, stock options granted $ 24,300,000impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateFairValue $ 7,300,000impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateFairValue $ 10,100,000impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGrantDateFairValue                  
Aggregate grant date fair value, stock options vested 7,200,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1 4,600,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1 2,100,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1                  
Intrinsic value of options exercised 14,700,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 23,200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 34,600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue                  
Compensation cost related to unvested stock-based awards granted, but not yet recognized 91,700,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions                      
Nonvested awards, compensation cost not yet recognized, period for recognition 2 years 10 months 24 days                      
Net cash proceeds from the exercise of stock options 8,500,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 6,300,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 4,200,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions                  
Capitalized stock-based compensation cost 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount                  
Recognized stock-based compensation tax benefits 385,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 19,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense                  
Weighted-average grant date fair value $ 41.66us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 36.94us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue                    
Unvested shares 2,279,081us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 1,044,651us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber 446,915us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber                  
Assumed common stock options in acquisitions 72,607us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod                      
Incapsula Acquisition [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Business acquisition purchase price, shares issued       124,088us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
/ us-gaap_BusinessAcquisitionAxis
= impv_IncapsulaAcquisitionMember		                
Skyfence Networks Ltd. [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Nonvested awards, compensation cost not yet recognized, period for recognition         4 years              
Business acquisition purchase price, shares issued         884,422us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
/ us-gaap_BusinessAcquisitionAxis
= impv_SkyfenceNetworksLtdMember		              
Closing price of stock         $ 59.08us-gaap_BusinessAcquisitionSharePrice
/ us-gaap_BusinessAcquisitionAxis
= impv_SkyfenceNetworksLtdMember		              
Common stock, shares vested 0us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares
/ us-gaap_BusinessAcquisitionAxis
= impv_SkyfenceNetworksLtdMember		                      
Incapsula [Member] | Skyfence Networks Ltd. [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Assumed common stock options in acquisitions 72,607us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod
/ us-gaap_BusinessAcquisitionAxis
= impv_SkyfenceNetworksLtdMember
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		                      
Stock options [Member] | Director [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Unvested shares 6,667us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		 45,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedNumberOfShares
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                    
Unvested shares, value 71,000impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		 400,000impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedIntrinsicValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember		                    
Restricted Stock Units for Common Stock [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of Restricted Stock Units Vested in Period $ 8,300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 $ 6,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 $ 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		                  
Restricted Stock Units for Common Stock [Member] | Incapsula [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Shares issuable, as-converted to common stock-basis   198,825us-gaap_ConversionOfStockSharesIssued1
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		                    
Restricted Stock Units And Options Outstanding [Member] | Incapsula [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Shares issuable, as-converted to common stock-basis 247,184us-gaap_ConversionOfStockSharesIssued1
/ us-gaap_AwardTypeAxis
= impv_RestrictedStockUnitsAndStockOptionMember
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember		                      
Restricted Shares of Common Stock Subject to Repurchase [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Performance-based restricted stock units granted 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		       843,819us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		            
Weighted-average grant date fair value           $ 1.94us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		            
Unvested shares 210,954us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		                      
Restricted Shares of Common Stock Subject to Repurchase [Member] | Skyfence Networks Ltd. [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Business acquisition purchase price, shares issued         532,262us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_BusinessAcquisitionAxis
= impv_SkyfenceNetworksLtdMember		              
Restricted Shares of Common Stock Subject to Repurchase [Member] | Minimum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period 48 months                      
Restricted Shares of Common Stock Subject to Repurchase [Member] | Maximum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period 60 months                      
2003 Stock Plan [Member] | Stock options [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Maximum percentage of fair value of common stock on grant date 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= impv_TwoThousandThreeStockPlanMember		                      
2003 Stock Plan [Member] | Stock options [Member] | Greater 10% Ownership [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Maximum percentage of fair value of common stock on grant date 110.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= impv_GreaterTenPercentOwnershipMember
/ us-gaap_PlanNameAxis
= impv_TwoThousandThreeStockPlanMember		                      
Minimum percentage of combined voting power 10.00%impv_MinimumPercentageOfCombinedVotingPower
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= impv_GreaterTenPercentOwnershipMember
/ us-gaap_PlanNameAxis
= impv_TwoThousandThreeStockPlanMember		                      
2003 Stock Plan [Member] | Stock options [Member] | Minimum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period 4 years                      
2003 Stock Plan [Member] | Stock options [Member] | Maximum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Expiration period 10 years                      
2011 Stock Option and Incentive Plan [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Reserve of common stock for future issuance                 1,000,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		      
Increase percentage of common stock outstanding 4.00%impv_IncreasePercentageOfCommonStockOutstanding
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		                      
Shares available for grant 1,166,742us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		                      
Increase in reserve share 1,075,819us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		                      
2011 Stock Option and Incentive Plan [Member] | Stock options [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Expiration period 10 years                      
Maximum percentage of fair value of common stock on grant date 100.00%impv_StockOptionsExercisePricePercentageOfFairMarketValueOfUnderlyingStockOnGrantDate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		                      
2011 Stock Option and Incentive Plan [Member] | Restricted Stock Units for Common Stock [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting period             4 years          
Description of vesting terms             The Company began granting RSUs in February 2012, which generally vest either over a four-year period with 25% vesting at the end of one year and the remainder vesting quarterly thereafter or they completely vest at the end of a three-year period.          
2011 Stock Option and Incentive Plan [Member] | Restricted Stock Units for Common Stock [Member] | Incapsula Acquisition [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Performance-based restricted stock units granted 264,878us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_BusinessAcquisitionAxis
= impv_IncapsulaAcquisitionMember
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember		                      
2011 Stock Option and Incentive Plan [Member] | Restricted Stock Units for Common Stock [Member] | Share-based Compensation Award, Tranche One [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting percentage at the end of period             25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= impv_StockOptionAndIncentivePlanMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheOneMember		          
2011 Employee Stock Purchase Plan [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Reserve of common stock for future issuance                 500,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember		      
Increase percentage of common stock outstanding               1.00%impv_IncreasePercentageOfCommonStockOutstanding
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember		        
Increase in reserve share 268,955us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember		                      
Percentage in payroll of deduction base salary to acquire shares of common stock                 15.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumEmployeeSubscriptionRate
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember		      
Offering period                 24 months      
Percentage of fair value of common stock on offering period                 85.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPriceOfferingDate
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember		      
Number of years, shares reserved for issuance will increase               8 years        
2011 Employee Stock Purchase Plan [Member] | Maximum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Reserve of common stock for future issuance                 20,000,000us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		      
Number of purchase periods for offering                 5impv_NumberOfPurchasePhaseForOffering
/ us-gaap_PlanNameAxis
= impv_TwoThousandElevenEmployeeStockPurchasePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		      
Incapsula 2010 Share Incentive Plan [Member] | Maximum [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Reserve of common stock for future issuance                       4,733,333us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= impv_IncapsulaTwoThousandTenShareIncentivePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Incapsula 2010 Share Incentive Plan [Member] | Restricted Stock Units for Common Stock [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Performance-based restricted stock units granted                   7,095,461us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= impv_IncapsulaTwoThousandTenShareIncentivePlanMember		    
Inducement Restricted Stock Unit Plan and Agreement [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Shares available for grant                     265,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= impv_InducementRestrictedStockUnitPlanAndAgreementMember		  
Description of vesting terms                     In accordance with the terms of the Inducement RSU Plan, the Company can issue RSUs representing a total of 265,000 shares of the Company's common stock (the RSUs"). The RSUs, which will expire following settlement, will vest at the rate of 25% of the shares on the first anniversary of the vesting commencement date with an additional 6.25% of the shares subject to the RSU vesting each quarter thereafter so long as participant has not been terminated.  
Inducement Restricted Stock Unit Plan and Agreement [Member] | Share-based Compensation Award, Tranche One [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting percentage at the end of period                     25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= impv_InducementRestrictedStockUnitPlanAndAgreementMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheOneMember		  
Inducement Restricted Stock Unit Plan and Agreement [Member] | Quarterly Vesting [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting percentage at the end of period                     6.25%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= impv_InducementRestrictedStockUnitPlanAndAgreementMember
/ us-gaap_VestingAxis
= impv_QuarterlyVestingMember		  
Inducement Stock Option Plan And Agreement [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Description of vesting terms                     In accordance with the terms of the Inducement Option Plan, the Company can issue an option to purchase up to 265,000 shares of the Company’s common stock at an exercise price equal to the fair market value of a share of the Company’s common stock on the date of grant of the option. The option, which will have a ten-year term, will vest at the rate of 25% of the shares on the first anniversary of the vesting commencement date with an additional 6.25% of the shares subject to the option vesting each quarter thereafter so long as the participant has not been terminated.  
Number of stock option outstanding, granted                     265,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= impv_InducementStockOptionPlanAndAgreementMember		  
Inducement Stock Option Plan And Agreement [Member] | Share-based Compensation Award, Tranche One [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting percentage at the end of period                     25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= impv_InducementStockOptionPlanAndAgreementMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheOneMember		  
Inducement Stock Option Plan And Agreement [Member] | Quarterly Vesting [Member]                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Vesting percentage at the end of period                     6.25%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= impv_InducementStockOptionPlanAndAgreementMember
/ us-gaap_VestingAxis
= impv_QuarterlyVestingMember