Capitalized stock-based compensation cost.

No definition available.

Name:	impv_CapitalizedStockBasedCompensationCost
Namespace Prefix:	impv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Increase percentage of common stock outstanding.

+ References

No definition available.

+ Details

Name:	impv_IncreasePercentageOfCommonStockOutstanding
Namespace Prefix:	impv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum percentage of fair value of common stock on grant date.

+ References

No definition available.

+ Details

Name:	impv_MaximumPercentageOfFairValueOfCommonStockOnGrantDate
Namespace Prefix:	impv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum percentage of combined voting power.

+ References

No definition available.

+ Details

Name:	impv_MinimumPercentageOfCombinedVotingPower
Namespace Prefix:	impv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of purchase period for offering.

+ References

No definition available.

+ Details

Name:	impv_NumberOfPurchasePeriodForOffering
Namespace Prefix:	impv_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of years, shares reserved for issuance will increase.

+ References

No definition available.

+ Details

Name:	impv_NumberOfYearsSharesReservedForIssuanceWillIncrease
Namespace Prefix:	impv_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage in payroll of deduction base salary to acquire shares of common stock.

+ References

No definition available.

+ Details

Name:	impv_PercentageInPayrollOfDeductionBaseSalaryToAcquireSharesOfCommonStock
Namespace Prefix:	impv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Restricted common stock unvested.

+ References

No definition available.

+ Details

Name:	impv_RestrictedCommonStockUnvested
Namespace Prefix:	impv_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment award options offering period.

+ References

No definition available.

+ Details

Name:	impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOfferingPeriod
Namespace Prefix:	impv_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award purchase price of common stock percent in voting power criteria.

+ References

No definition available.

+ Details

Name:	impv_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePriceOfCommonStockPercentInVotingPowerCriteria
Namespace Prefix:	impv_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	impv_StockPlansTextualAbstract
Namespace Prefix:	impv_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Unvested shares.

+ References

No definition available.

+ Details

Name:	impv_UnvestedShares
Namespace Prefix:	impv_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate unrecognized cost of option awards made to employees under a stock option plan or plans, that have yet to vest.

+ References

No definition available.

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph g(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph b(2)(c)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Purchase price of common stock expressed as a percentage of its fair market value.

+ References

No definition available.

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Stock Plans (Details Textual) (USD $)	9 Months Ended						1 Months Ended	9 Months Ended		1 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended		9 Months Ended
Stock Plans (Details Textual) (USD $)	Sep. 30, 2012 2003 Stock Plan [Member]	Sep. 30, 2012 2003 Stock Plan [Member] Maximum [Member]	Sep. 30, 2012 2003 Stock Plan [Member] Minimum [Member]	Sep. 30, 2012 2011 Stock Option [Member]	Dec. 31, 2011 2011 Stock Option [Member]	Sep. 09, 2011 2011 Stock Option [Member]	Sep. 30, 2011 2011 Employee Stock Purchase Plan [Member]	Sep. 30, 2012 2011 Employee Stock Purchase Plan [Member]	Sep. 09, 2011 2011 Employee Stock Purchase Plan [Member]	Sep. 30, 2011 2011 Employee Stock Purchase Plan [Member] Maximum [Member] Period	Sep. 30, 2012 2011 Employee Stock Purchase Plan [Member] Maximum [Member]	Sep. 30, 2012 Incapsula 2010 Share Incentive Plan [Member]	Sep. 30, 2011 Incapsula 2010 Share Incentive Plan [Member]	Mar. 31, 2010 Incapsula 2010 Share Incentive Plan [Member] Maximum [Member]	Sep. 30, 2012 Common Stock Subject to Repurchase [Member]	Dec. 31, 2011 Common Stock Subject to Repurchase [Member]	Dec. 31, 2010 Common Stock Subject to Repurchase [Member]	Sep. 30, 2012 Common Stock Subject to Repurchase [Member] Maximum [Member]	Sep. 30, 2012 Common Stock Subject to Repurchase [Member] Minimum [Member]	Sep. 30, 2012 Early Exercise of Stock Options [Member]
Stock Plans (Textual) [Abstract]
Maximum percentage of fair value of common stock on grant date	85.00%						85.00%
Minimum percentage of combined voting power	10.00%
Maximum percentage of option price of fair value	110.00%
Reserve of common stock issuance						1,000,000			500,000		20,000,000			4,733,333
Increase percentage of common stock outstanding				4.00%				1.00%
Shares available for grant					1,886,296
Increase in reserve share				919,127				229,782
Maximum percentage of fair value of common stock on grant date				100.00%
Percentage in payroll of deduction base salary to acquire shares of common stock							15.00%
Offering period										24 months
Number of purchase period for offering										5
Intrinsic value of option exercised												$ 29,000,000
Number of years, shares reserved for issuance will increase								8 years
Market value of common stock												$ 36.99
Compensation cost related to unvested stock based awards granted, but not yet recognized												16,400,000
Nonvested awards, compensation cost not yet recognized, period for recognition												2 years 4 months 24 days
Capitalized stock-based compensation cost												0	0
Recognized stock-based compensation tax benefits												$ 0	$ 0
Vesting Period		10 years	4 years	10 years														60 months	48 months
Restricted common stock granted															0	0	843,819
Weighted-average grant date fair value																	$ 1.94
Restricted common stock unvested															487,833
Unvested shares																				91,875