Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Business	Business Imperva, Inc. (together with its subsidiaries, the “Company”) was incorporated in April 2002 in Delaware. The Company is headquartered in Redwood Shores, California and has subsidiaries located throughout the world including Israel, Asia and Europe. The Company is engaged in the development, marketing, sales, service and support of cyber-security solutions that protect business-critical data and applications whether in the cloud or on premises.
Basis of Presentation	Basis of Presentation The Company has prepared the accompanying unaudited Condensed Consolidated Financial Statements in accordance with Article 10 of Regulation S-X and pursuant to the rules and regulations for Form 10-Q of the Securities and Exchange Commission (the “SEC”). Pursuant to those rules and regulations, the Company has condensed or omitted certain information and footnote disclosure it normally includes in its annual consolidated financial statements prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). In management’s opinion, the Company has made all adjustments (consisting only of normal, recurring adjustments, except as otherwise indicated) necessary to fairly present its consolidated financial position, results of operations, and cash flows. The Company’s interim period operating results do not necessarily indicate the results that may be expected for any other interim period or for the full fiscal year. These financial statements and accompanying notes should be read in conjunction with the consolidated financial statements and notes thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, which was filed with the SEC on February 27, 2017 (the “Annual Report”). The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Concentration of Revenue and Accounts Receivable	Concentration of Revenue and Accounts Receivable Significant customers are those which represent 10% or more of the Company’s total revenue or gross accounts receivable balance at each respective balance sheet date. For the three months ended March 31, 2017 and 2016, the Company had one customer that represented 11% and 14% of the Company’s total revenue, respectively. The same customer represented 11% and 18% of accounts receivable as of March 31, 2017 and December 31, 2016, respectively. A different customer represented 10% and 9% of accounts receivable as of March 31, 2017 and December 31, 2016, respectively.
Significant Accounting Policies	Significant Accounting Policies The Company adopted the guidance in Accounting Standards Update (“ASU”) 2016-09, Compensation - Stock Compensation (Topic 718) - Improvements to Employee Share-Based Payment Accounting, on January 1, 2017. Under this ASU, entities are permitted to make an accounting policy election to either estimate forfeitures on share-based payment awards, as previously required, or to recognize forfeitures as they occur. The Company has elected to recognize forfeitures as they occur and the impact of that change in accounting policy has been recorded as a $2.6 million cumulative effect adjustment to increase our accumulated deficit as of January 1, 2017. Additionally, the Company has elected to use a prospective transition method for presentation of excess tax benefits on the statement of cash flows. The remaining provisions of ASU 2016-09 did not have a material impact on the accompanying condensed consolidated financial statements. There have been no other material changes to the Company’s significant accounting policies as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In January 2017, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment (Topic 350), which simplifies the measurement of goodwill impairment by removing the second step of the goodwill impairment test, which requires the determination of the fair value of individual assets and liabilities of a reporting unit. Under this guidance, goodwill impairment is to be measured as the amount by which a reporting unit’s carrying value exceeds its fair value with the loss recognized not to exceed the total amount of goodwill allocated to the reporting unit. The guidance is effective beginning January 1, 2020 on a prospective basis, with early adoption permitted for interim or annual goodwill impairment tests performed after January 1, 2017. The standard is to be applied on a prospective basis. The Company does not anticipate a material impact to the consolidated financial statements once implemented. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The new standard provides a screen to determine when a set of activities and assets, or “set,” is not a business. The screen requires that when substantially all of the fair value of the gross assets acquired (or disposed of) is concentrated in a single identifiable asset or a group of similar identifiable assets, the set is not a business. This screen reduces the number of transactions that need to be further evaluated. If the screen is not met, the amendments in this ASU: (1) require that to be considered a business, a set must include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output, and (2) remove the evaluation of whether a market participant could replace missing elements. The amendments provide a framework to assist entities in evaluating whether both an input and a substantive process are present. The framework includes two sets of criteria to consider that depend on whether a set has outputs. Although outputs are not required for a set to be a business, outputs generally, are a key element of a business; therefore, the Board has developed more stringent criteria for sets without outputs. Lastly, the amendments in this ASU narrow the definition of the term output so that the term is consistent with how outputs are described in Topic 606. The standard will be effective for the Company beginning January 1, 2018, with early application permitted. The standard will require adoption on a prospective basis. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. The new standard requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The standard will be effective for the Company beginning January 1, 2018, with early application permitted. The standard will require adoption on a retrospective basis. The new accounting pronouncements will not have a significant impact on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The new standard will make eight targeted changes to how cash receipts and cash payments are presented and classified in the statement of cash flows. The standard will be effective for the Company beginning January 1, 2018, with early application permitted. The standard will require adoption on a retrospective basis unless it is impracticable to apply, in which case we would be required to apply the amendments prospectively as of the earliest date practicable. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements. In June 2016, the FASB Issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard requires financial assets measured at amortized cost be presented at the net amount expected to be collected, through an allowance for credit losses that is deducted from the amortized cost basis. The standard will be effective for the Company beginning January 1, 2020, with early application permitted. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02 regarding ASC Topic 842 “Leases.” The amendments in this guidance require balance sheet recognition of lease assets and lease liabilities by lessees for leases classified as operating leases, with an optional policy election to not recognize lease assets and lease liabilities for leases with a term of 12 months or less. The amendments also require new disclosures, including qualitative and quantitative requirements, providing additional information about the amounts recorded in the financial statements. The standard will be effective for the Company beginning January 1, 2019. The amendments require a modified retrospective approach with optional practical expedients. The Company is evaluating the impact of adopting this new accounting guidance on its consolidated financial statements. In May 2014, the FASB issued ASU 2014-09—Revenue (Topic 606): Revenue from Contracts with Customers. The standard will replace most existing U.S. GAAP guidance on this topic. The standard provides a unified model to determine when and how revenue is recognized. The core principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. The standard defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing GAAP, including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation, among others. The standard also provides guidance on the recognition of costs related to obtaining customer contracts. The standard will be effective for the Company beginning January 1, 2018 using either of two methods: (1) retrospective application of the standard to each prior reporting period presented with the option to elect certain practical expedients as defined within the standard, or (2) retrospective application of the standard with the cumulative effect of initially applying the standard recognized at the date of initial application and providing certain additional disclosures as defined per the standard. Adoption as of the original effective date of January 1, 2017 is permitted. The Company is considering adopting the standard under the modified retrospective method effective January 1, 2018; however, a final decision regarding the adoption method has not been finalized at this time. The Company’s ability to adopt using the modified retrospective method is dependent on several factors such as the significance of the impact of the new standard on the Company’s financial results, and system readiness. The Company has developed a project plan for this transition, which includes necessary changes to accounting policies, processes, and system requirements. The Company expects to implement the plan in time to report in accordance with ASC 606 for the first quarterly filing on Form 10-Q for the period ended March 31, 2018. As part of its preliminary evaluation, the Company has considered the impact of the standard’s requirements with respect to capitalization and amortization of incremental costs of obtaining a contract, primarily sales commissions. Under the Company’s current accounting policy, contract origination costs are expensed as incurred. The new standard requires the capitalization of all incremental costs that the Company incurs to obtain a contract with a customer that it would not have incurred if the contract had not been obtained, provided the Company expects to recover the costs. While the Company continues to assess the potential impacts of the new standard, the Company does not know or cannot reasonably estimate quantitative information related to the impact of the new standard on the financial statements at this time.