Capital Stock - Option and Performance-Based Restricted Share Unit Activity Under Incapsula Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Restricted Stock Units Outstanding, Unvested - Beginning Balance	1,044,651	446,915
Number of Restricted Stock Units Outstanding, Granted	1,368,761	577,528
Number of Restricted Stock Units Outstanding, Exercised/Released	238,446	149,531
Number of Restricted Stock Units Outstanding, Forfeited	(225,853)	(95,139)
Number of Restricted Stock Units Outstanding, Unvested - Ending balance	2,279,081	1,044,651	446,915
Number of Stock Options Outstanding, Outstanding - Beginning balance	1,675,506	1,989,237	2,871,005
Number of Stock Options Outstanding, Granted	1,256,559	631,775	698,240
Number of Stock Options Outstanding, Exercised/Released	(496,297)	(687,719)	(1,272,941)
Number of Stock Options Outstanding, Forfeited	(264,012)	(257,787)	(307,067)
Number of Stock Options Outstanding, Outstanding - Ending balance	2,244,363	1,675,506	1,989,237
Weighted Average Exercise Price of Stock Options Outstanding, Beginning balance	$ 23.78	$ 14.08	$ 4.15
Weighted Average Exercise Price of Stock Options Outstanding, Granted	$ 41.39	$ 36.55	$ 31.80
Weighted Average Exercise Price of Stock Options Outstanding, Exercised/Released	$ 14.85	$ 6.94	$ 2.41
Weighted Average Exercise Price of Stock Options Outstanding, Forfeited	$ 35.85	$ 25.11	$ 9.98
Weighted Average Exercise Price of Stock Options Outstanding, Ending balance	$ 33.83	$ 23.78	$ 14.08
Incapsula Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Outstanding - Beginning Balance	89,687	2,753,708	2,921,833
Additional shares authorized		5,529,878
Shares Available for Grant, Granted	(95,000)		(232,500)
Shares Available for Grant, Exercised/Released		0	0
Shares Available for Grant, Forfeited	15,213	141,562	64,375
Shares Available for Grant, Transferred to Imperva 2011 stock option plan	(9,900)
Shares Available for Grant, Outstanding - Ending Balance	0	89,687	2,753,708
Number of Stock Options Outstanding, Outstanding - Beginning balance	1,806,500	1,836,500	1,774,000
Number of Stock Options Outstanding, Granted	95,000		232,500
Number of Stock Options Outstanding, Exercised/Released		(1,128,438)	(105,625)
Number of Stock Options Outstanding, Forfeited	(2,500)	(141,562)	(64,375)
Number of Stock Options Outstanding, Transferred to Imperva 2011 stock option plan	(1,899,000)
Number of Stock Options Outstanding, Outstanding - Ending balance	0	1,806,500	1,836,500
Weighted Average Exercise Price of Stock Options Outstanding, Beginning balance	$ 0.47	$ 0.10	$ 0.08
Weighted Average Exercise Price of Stock Options Outstanding, Granted	$ 1.25		$ 0.25
Weighted Average Exercise Price of Stock Options Outstanding, Exercised/Released		$ 0.02	$ 0.15
Weighted Average Exercise Price of Stock Options Outstanding, Forfeited	$ 1.25	$ 0.22	$ 0.18
Weighted Average Exercise Price of Stock Options Outstanding, Transferred to Imperva 2011 stock option plan	$ 0.16
Weighted Average Exercise Price of Stock Options Outstanding, Ending balance	$ 0	$ 0.47	$ 0.10
Incapsula Plan [Member] | Performance RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Restricted Stock Units Outstanding, Additional Stock authorized		0
Shares Available for Grant, Granted		(7,095,461)
Number of Restricted Stock Units Outstanding, Unvested - Beginning Balance	7,095,461	0	0
Number of Restricted Stock Units Outstanding, Granted	0	7,095,461	0
Number of Restricted Stock Units Outstanding, Exercised/Released		0	0
Number of Restricted Stock Units Outstanding, Forfeited	(12,713)	0	0
Number of Restricted Stock Units Outstanding, Transferred to Imperva 2011 stock option plan	(7,082,748)
Number of Restricted Stock Units Outstanding, Unvested - Ending balance	0	7,095,461	0
Number of Stock Options Outstanding, Granted		0
Weighted Average Exercise Price of Stock Options Outstanding, Granted		$ 0
Incapsula Plan [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Granted		(1,240,000)
Number of Restricted Stock Units Outstanding, Granted		0
Number of Stock Options Outstanding, Granted		1,240,000
Weighted Average Exercise Price of Stock Options Outstanding, Granted		$ 0.58