Stock Plans - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			0 Months Ended	3 Months Ended		3 Months Ended	12 Months Ended			3 Months Ended					12 Months Ended		3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended		12 Months Ended			1 Months Ended			3 Months Ended		3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Feb. 07, 2014 SkyFence Networks Ltd. [Member]	Mar. 31, 2014 Incapsula [Member] SkyFence Networks Ltd. [Member]	Mar. 31, 2014 Stock options [Member] Director [Member]	Mar. 31, 2014 Restricted shares of common stock subject to repurchase [Member]	Dec. 31, 2013 Restricted shares of common stock subject to repurchase [Member]	Dec. 31, 2012 Restricted shares of common stock subject to repurchase [Member]	Dec. 31, 2010 Restricted shares of common stock subject to repurchase [Member]	Mar. 31, 2014 Restricted shares of common stock subject to repurchase [Member] Minimum [Member]	Mar. 31, 2014 Restricted shares of common stock subject to repurchase [Member] Maximum [Member]	Mar. 31, 2014 2003 stock plan [Member] Stock options [Member]	Mar. 31, 2014 2003 stock plan [Member] Stock options [Member] Minimum [Member]	Mar. 31, 2014 2003 stock plan [Member] Stock options [Member] Maximum [Member]	Dec. 31, 2013 2011 stock option and incentive plan [Member]	Sep. 30, 2011 2011 stock option and incentive plan [Member]	Mar. 31, 2014 2011 stock option and incentive plan [Member] Stock options [Member]	Feb. 29, 2012 2011 stock option and incentive plan [Member] Restricted stock units for common stock [Member]	Mar. 31, 2014 2011 stock option and incentive plan [Member] Restricted stock units for common stock [Member] Incapsula acquisition [Member]	Jan. 31, 2012 2011 employee stock purchase plan [Member]	Sep. 30, 2011 2011 employee stock purchase plan [Member]	Dec. 31, 2013 2011 employee stock purchase plan [Member]	Dec. 31, 2012 2011 employee stock purchase plan [Member]	Mar. 31, 2014 2011 employee stock purchase plan [Member]	Sep. 30, 2011 2011 employee stock purchase plan [Member] Maximum [Member] Period	Dec. 31, 2013 2011 employee stock purchase plan [Member] Maximum [Member]	Mar. 31, 2010 Incapsula 2010 share incentive plan [Member]	Mar. 31, 2014 Incapsula 2010 share incentive plan [Member] Restricted stock units for common stock [Member]	Nov. 30, 2013 Incapsula 2010 share incentive plan [Member] Restricted stock units for common stock [Member]	Mar. 31, 2014 2003 stock and 2011 Imperva stock option and incentive plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of fair value of common stock on grant date													85.00%
Minimum percentage of combined voting power													10.00%
Maximum percentage of option price of fair value													110.00%
Vesting period	4 years										48 months	60 months		4 years	10 years
Reserve of common stock for future issuance																	1,000,000								500,000		20,000,000	4,733,333
Increase percentage of common stock outstanding																4.00%					1.00%
Shares available for grant																1,847,752														7,095,461
Increase in reserve share																1,008,260							252,065	242,961
Maximum percentage of fair value of common stock on grant date																		100.00%				85.00%
Expiration period																		10 years
Vesting period of RSUs																			4 years
Vesting percentage at each year																			25.00%
Remaining vesting period of RSUs																			3 years
Performance-based restricted stock units granted	582,952						0	0	0	843,819										264,878									253,187
Percentage in payroll of deduction base salary to acquire shares of common stock																						15.00%
Offering period																						24 months
Number of purchase periods for offering																										5
Number of years, shares reserved for issuance will increase																					8 years
Common stock, shares vested																													204,828
Intrinsic value of options exercised																															$ 7.7
Market value of common stock																															$ 55.70
Compensation cost related to unvested stock-based awards granted, but not yet recognized				1.1																											95.0
Nonvested awards, compensation cost not yet recognized, period for recognition																															2 years 10 months 24 days
Capitalized stock-based compensation cost	$ 0	$ 0
Weighted-average grant date fair value										$ 1.94
Restricted common stock unvested	250,500
Business acquisition, shares for forfeiture	532,262			532,262
Closing price of stock	$ 59.08			$ 59.08
Common stock, shares vested	0
Unvested shares	1,718,553		1,044,651			35,625
Assumed common stock options in acquisitions	72,607				72,607