Fair Value of Financial Instruments - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value transfer between Levels	$ 0impv_FairValueTransfer	$ 0impv_FairValueTransfer
Level II [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Severance pay assets	$ 4,000,000	$ 4,100,000

Represents the fair value of insurance policies purchased to satisfy liabilities related to certain retired or dismissed Israeli employees.

No definition available.

Name:	impv_SeverancePayAssetsFairValue
Namespace Prefix:	impv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant