Stock Plans - Option and Performance-Based Restricted Share Unit Activity under Incapsula Plan (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Stock Options Outstanding, - Beginning Balance	1,675,506
Number of Stock Options Outstanding, Granted	1,076,327
Number of Stock Options Outstanding, Exercised	(311,650)
Number of Stock Options Outstanding, Forfeited	(213,947)
Number of Stock Options Outstanding, - Ending Balance	2,298,843
Options Outstanding, weighted Average Exercise Price - Beginning Balance	$ 23.78
Weighted Average Exercise Price, Granted	$ 42.37
Weighted Average Exercise Price, Exercised	$ 10.60
Weighted Average Exercise Price, Forfeited	$ 34.81
Options Outstanding, weighted Average Exercise Price - Ending Balance	$ 32.89
Incapsula Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Outstanding - Beginning Balance	89,687
Shares Available for Grant, Granted	(95,000)
Shares Available for Grant, Exercised	0
Shares Available for Grant, Forfeited	15,213
Shares Available for Grant, Transferred to Imperva 2011 stock option plan	(9,900)
Shares Available for Grant, Outstanding - Ending Balance	0
Number of Performance-based Restricted Share Units Outstanding - Beginning Balance	7,095,461
Number of Performance-based Restricted Share Units Outstanding, Granted	0
Number of Performance-based Restricted Share Units Outstanding, Exercised	0
Number of Performance-based Restricted Share Units Outstanding, Forfeited	(12,713)
Number of Performance-based Restricted Share Units Outstanding, Transferred to Imperva 2011 stock option plan	(7,082,748)
Number of Performance-based Restricted Share Units Outstanding - Ending Balance	0
Number of Stock Options Outstanding, - Beginning Balance	1,806,500
Number of Stock Options Outstanding, Granted	95,000
Number of Stock Options Outstanding, Exercised	0
Number of Stock Options Outstanding, Forfeited	(2,500)
Number of Stock Options Outstanding, Transferred to Imperva 2011 stock option plan	(1,899,000)
Number of Stock Options Outstanding, - Ending Balance	0
Options Outstanding, weighted Average Exercise Price - Beginning Balance	$ 0.47
Weighted Average Exercise Price, Granted	$ 1.25
Weighted Average Exercise Price, Exercised	$ 0.00
Weighted Average Exercise Price, Forfeited	$ 1.25
Weighted Average Exercise Price, Transferred to Imperva 2011 stock option plan	$ 0.16
Options Outstanding, weighted Average Exercise Price - Ending Balance	$ 0.00