Employee service share based compensation tax expense (benefit) from compensation expense.

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Maximum offering period for the employee stock purchase plan.

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- Definition

The percentage increase of common stock outstanding.

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- Definition

Minimum Percentage Of Combined Voting Power

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- Definition

Number of years at the beginning of which the number of shares reserved will be increased.

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Maximum number of purchases over the offering period.

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- Definition

Share based compensation arrangement by share based payment award effective date.

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- Definition

Number of shares of equity interests issued or issuable to acquire entity.

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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Aggregate number of common shares reserved for future issuance.

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The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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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.

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- Definition

The cash outflow for cost incurred directly with the issuance of an equity security.

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The cash inflow from the additional capital contribution to the entity.

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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.

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Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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- Definition

Discount rate from fair value on offering date that participants pay for shares.

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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).

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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- Definition

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

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No definition available.

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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.

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

Gross number of share options (or share units) granted during the period.

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No definition available.

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Percentage of vesting of share-based compensation awards.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of options vested.

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No definition available.

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- Definition

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

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No definition available.

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- Definition

Per share or per unit amount of equity securities issued.

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- Definition

Number of new stock issued during the period.

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Stock Plans - Additional Information (Detail)		1 Months Ended						3 Months Ended			9 Months Ended
Stock Plans - Additional Information (Detail)	Jan. 01, 2016 shares	May 31, 2016 shares	Oct. 31, 2015 shares	Aug. 31, 2014 shares	Nov. 30, 2013 shares	Jan. 31, 2012	Sep. 30, 2011 Period shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock option outstanding, granted								0			48,260
Performance-based restricted stock units granted											929,168
Capitalized stock-based compensation expense \| $											$ 0	$ 0
Recognized stock-based compensation tax deficiencies (benefits) \| $								$ 15,000	$ (17,000)		29,000	(60,000)
Aggregate net proceeds from sale of common stock, net of underwriting discounts, commissions and offering costs \| $											8,106,000	12,668,000
Underwriting discounts, commissions and other offering expenses \| $											$ 112,000	$ 0
Follow-On Public Offering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock, shares										3,450,000
Sale of common stock, price per share \| $ / shares										$ 39.00
Aggregate net proceeds from sale of common stock, net of underwriting discounts, commissions and offering costs \| $										$ 127,900,000
Underwriting discounts, commissions and other offering expenses \| $										$ 6,700,000
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											532,262
Closing price of stock \| $ / shares								$ 59.08			$ 59.08
Common stock, shares vested											236,537
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					198,825
Outstanding Options and RSUs [Member] \| Incapsula [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issuable, as-converted to common stock-basis											247,184
2003 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in reserve share							955,568
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%
2003 Stock Plan [Member] \| Stock options [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period											10 years
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] \| Greater 10% Ownership [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											110.00%
Minimum percentage of combined voting power											10.00%
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							1,000,000
Increase in reserve share		1,300,000
Increase percentage of common stock outstanding											4.00%
2011 Stock Option and Incentive 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											100.00%
Expiration period											10 years
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 also grants RSUs, which generally vest over either 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] \| 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%
2011 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance							500,000
Increase in reserve share	318,371
Increase percentage of common stock outstanding						1.00%
Program effective date							Nov. 08, 2011
Percentage in payroll of deduction base salary to acquire shares of common stock							15.00%
Offering period							24 months
Percentage of fair value of common stock on offering period							85.00%
Number of years, shares reserved for issuance 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							20,000,000
Number of purchase periods for offering \| Period							5
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 Plans, the Company issued options to purchase up to 290,000 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 dates of grant of the options. The options, which have a ten-year term, vest at the rate of 25% of the shares on each of 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				290,000
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%
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%
Inducement Restricted Stock Unit 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 RSU Plans, the Company issued RSUs representing a total of 290,000 shares of the Company’s common stock. The RSUs, which expire following settlement, vest at the rate of 25% of the shares on each of 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 the participant has not been terminated.
Shares available for grant				290,000
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%
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%
2015 Equity Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reserve of common stock for future issuance			100,000
2015 Equity Inducement 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			100.00%
Expiration period			10 years
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					10,263,211
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					7,095,461
2003 Stock and 2011 Imperva Stock Option and Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised \| $											$ 2,100,000
Compensation cost related to unvested stock-based awards granted, but not yet recognized \| $								$ 87,000,000			$ 87,000,000
Nonvested awards, compensation cost not yet recognized, period for recognition											2 years 6 months