Incapsula - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended			1 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended	0 Months Ended					0 Months Ended		1 Months Ended
	Mar. 31, 2014	Sep. 30, 2014	Dec. 31, 2013		Mar. 31, 2014 Incapsula [Member]	Mar. 31, 2014 Incapsula [Member] Assumed Outstanding Options [Member]	Dec. 31, 2013 Incapsula [Member] Restricted Stock Units for Common Stock [Member]	Mar. 31, 2014 Incapsula [Member] 15-Month Holdback [Member]	Dec. 31, 2013 Imperva [Member] Restricted Stock Units for Common Stock [Member]	Mar. 09, 2010 Series A Convertible Preferred Stock [Member]	Nov. 05, 2009 Series A Convertible Preferred Stock [Member]	Sep. 30, 2014 Series A Convertible Preferred Stock [Member]	Mar. 09, 2010 Series A Convertible Preferred Stock [Member]	Nov. 05, 2009 Series A Convertible Preferred Stock [Member]	Mar. 09, 2010 Series A-1 Convertible Preferred Stock [Member] Forward Contract [Member]	Mar. 09, 2010 Series A-1 Convertible Preferred Stock [Member] Forward Contract [Member]	Jan. 31, 2012 Series A-1 Preferred Stock [Member]	Jul. 31, 2011 Series A-1 Preferred Stock [Member]
Subsidiary or Equity Method Investee [Line Items]
Equity method investments, shares										6,666,666	5,000,000						4,375,000	4,375,000
Ownership interest													76.00%	58.00%			85.00%	82.00%
Value assigned to license														$ 0
Net assets														0
Value of goodwill on the acquisition date		34,972,000	0	[1]										0
Cash consideration										3,000,000							3,500,000	3,500,000
Number of shares to be purchased if certain milestones were achieved															8,750,000
Cash consideration for milestones achieved																7,000,000
Value assigned to forward contract																0
Purchase Right valuation description		Exercise of the Purchase Right was solely within the Company's control and the price for the remaining ownership interest was to be based on an Incapsula enterprise valuation calculated as the greater of (i) eight times Incapsula's prior 12 months trailing revenues or (ii) seven times the aggregate amount Incapsula had raised in connection with its Series A Convertible Preferred Stock financings.
Value assigned to Purchase Right												0
Amount paid for remaining outstanding capital stock					7,700,000
Business acquisition, shares issued					124,088	48,359			264,878
Common stock subject to holdback								34,485
Common stock subject to holdback, period					15 months
Shares issuable, as-converted to common stock-basis							198,825
Non-controlling interest reclassified to additional paid-in capital	$ 2,827,000

[1] The Condensed Consolidated Balance Sheet as of December 31, 2013 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.