Stock Plans - Option and Performance-Based Restricted Share Unit Activity under Incapsula Plan (Detail) (USD $)	3 Months Ended
	Mar. 31, 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	579,705
Number of Stock Options Outstanding, Exercised	168,247
Number of Stock Options Outstanding, Forfeited	(45,576)
Number of Stock Options Outstanding, - Ending Balance	2,113,995
Options Outstanding, weighted Average Exercise Price - Beginning Balance	$ 23.78
Weighted Average Exercise Price of Stock Options Outstanding, Granted	$ 55.79
Weighted Average Exercise Price of Stock Options Outstanding, Exercised	$ 14.69
Weighted Average Exercise Price of Stock Options Outstanding, Forfeited	$ 29.18
Options Outstanding, weighted Average Exercise Price - Ending Balance	$ 32.83
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
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
Number of Performance-based Restricted Share Units Outstanding - Beginning Balance	7,095,461
Number of Performance-based Restricted Share Units Outstanding, Granted
Number of Performance-based Restricted Share Units Outstanding, Exercised
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
Number of Stock Options Outstanding, - Beginning Balance	1,806,500
Number of Stock Options Outstanding, Granted	95,000
Number of Stock Options Outstanding, Exercised
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
Options Outstanding, weighted Average Exercise Price - Beginning Balance	$ 0.47
Weighted Average Exercise Price of Stock Options Outstanding, Granted	$ 1.25
Weighted Average Exercise Price of Stock Options Outstanding, Exercised
Weighted Average Exercise Price of Stock Options Outstanding, Forfeited	$ 1.25
Weighted Average Exercise Price of Stock Options Outstanding, Transferred to Imperva 2011 stock option plan	$ 0.16
Options Outstanding, weighted Average Exercise Price - Ending Balance