Acquisitions - Additional Information (Detail) - USD ($)			11 Months Ended	12 Months Ended
	Feb. 07, 2014	Jan. 30, 2014	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Residual value of intangible assets				$ 0
Business acquisition purchase price, cash paid				$ 0	$ 12,083,000	$ 0
Compensation expense, service period				2 years 7 months 6 days
Recognized compensation expense				$ 50,964,000	$ 37,273,000	$ 22,494,000
Maximum [Member]
Business Acquisition [Line Items]
Estimated useful life				10 years
Skyfence Networks Ltd. [Member]
Business Acquisition [Line Items]
Date of acquisition				Feb. 07, 2014
Business acquisition purchase price, cash paid	$ 8,558,000
Holdback payment commitment period	24 months
Holdback liability	$ 7,157,000
Business acquisition purchase price, shares issued	884,422
Compensation expense, service period	4 years
Closing price of stock	$ 59.08
Unvested equity awards to be recorded as operating expense	$ 1,100,000
Vested equity awards	300,000
Related acquisition costs	900,000
Recognized compensation expense			$ 7,300,000
Total purchase price	36,924,000
Business acquisition purchase price, common stock value	$ 20,855,000
Skyfence Networks Ltd. [Member] | Purchased Technology [Member]
Business Acquisition [Line Items]
Estimated useful life	7 years
Skyfence Networks Ltd. [Member] | Subject to a Holdback [Member]
Business Acquisition [Line Items]
Business acquisition purchase price, shares issued	29,871
Skyfence Networks Ltd. [Member] | Restricted Shares of Common Stock Subject to Repurchase [Member]
Business Acquisition [Line Items]
Business acquisition purchase price, shares issued	532,262
Skyfence Networks Ltd. [Member] | Skyfence Options [Member]
Business Acquisition [Line Items]
Options converted to purchase shares	164,000
Skyfence Networks Ltd. [Member] | Converted Imperva Options [Member]
Business Acquisition [Line Items]
Options converted to purchase shares	24,248
Skyfence Networks Ltd. [Member] | Maximum [Member]
Business Acquisition [Line Items]
Common stock subject to holdback, period	24 months
Tomium Software, LLC. [Member]
Business Acquisition [Line Items]
Date of acquisition				Jan. 30, 2014
Business acquisition purchase price, cash paid		$ 4,600,000
Business acquisition purchase price, shares issued		60,556
Closing price of stock		$ 55.45
Related acquisition costs		$ 300,000
Estimated useful life		10 years
Total purchase price		$ 8,263,000
Business acquisition purchase price, assumption of liability to pay cash		300,000
Business acquisition purchase price, common stock value		$ 3,400,000