Derivative Instruments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Forward foreign exchange contracts maturity	12 months

The contractual period to maturity of forward foreign exchange contracts.

No definition available.

Name:	impv_DerivativeForwardExchangeContractPeriod
Namespace Prefix:	impv_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration