Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies As permitted by the rules of the Securities and Exchange Commission applicable to Quarterly Reports on Form 10-Q, these notes are condensed and do not contain all disclosures required by generally accepted accounting principles (GAAP). As a result of the adoption of ASC 842 "Leases," Cognex Corporation (the "Company") has provided new disclosures related to leases in this Quarterly Report on Form 10-Q. Reference should be made to the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 for a full description of other significant accounting policies. In the opinion of the management of the Company, the accompanying consolidated unaudited financial statements contain all adjustments, consisting of normal, recurring adjustments, and financial statement reclassifications necessary to present fairly the Company’s financial position as of June 30, 2019, and the results of its operations for the three-month and six-month periods ended June 30, 2019 and July 1, 2018, and changes in shareholders’ equity, comprehensive income, and cash flows for the periods presented. The results disclosed in the Consolidated Statements of Operations for the three-month and six-month periods ended June 30, 2019 are not necessarily indicative of the results to be expected for the full year. Leases The Company accounts for leases in accordance with Accounting Standard Codification (ASC) 842, "Leases." The core principle of ASC 842 is that a lessee should recognize on the balance sheet the assets and liabilities that arise from leases. At inception of a contract, the Company determines whether that contract is or contains a lease. The Company determines whether a contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset for a period of time in exchange for consideration. The Company has control of the asset if it has the right to direct the use of the asset and obtains substantially all of the economic benefits from the use of the asset throughout the period of use. As a practical expedient, the Company does not recognize a lease asset or lease liability for leases with a lease term of 12 months or less. In the determination of the lease term, the Company considers the existence of extension or termination options and the probability of those options being exercised. Lease contracts may include lease components and non-lease components, such as common area maintenance and utilities for property leases. As a practical expedient, the Company accounts for the non-lease components together with the lease components as a single lease component for all of its leases. The Company classifies a lease as a finance lease when it meets any of the following criteria at the lease commencement date: a) the lease transfers ownership of the underlying asset to the Company by the end of the lease term; b) the lease grants the Company an option to purchase the underlying asset that the Company is reasonably certain to exercise; c) the lease term is for the major part of the remaining economic life of the underlying asset (the Company considers a major part to be 75% or more of the remaining economic life of the underlying asset); d) the present value of the sum of the lease payments and any residual value guaranteed by the Company equals or exceeds substantially all of the fair value of the underlying asset (the Company considers substantially all the fair value to be 90% or more of the fair value of the underlying asset amount); or e) the underlying asset is of such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. When none of the criteria above are met, the Company classifies the lease as an operating lease. On the lease commencement date, the Company records a lease asset and lease liability on the balance sheet. The lease asset consists of: 1) the amount of the initial lease liability; 2) any lease payments made to the lessor at or before the lease commencement date, minus any lease incentives received; and 3) any initial direct cost incurred by the Company. Initial direct costs are incremental costs of a lease that would not have been incurred if the lease had not been obtained and are capitalized as part of the lease asset. The lease liability equals the present value of the future cash payments discounted using the Company's incremental borrowing rate. The Company’s incremental borrowing rate is the rate of interest that the Company would have to pay to borrow an amount equal to the lease payments over a similar term, which is the three-month London Interbank Offered Rate (LIBOR) plus a 2.5% credit risk spread. Operating lease expense equals the total cash payments recognized on a straight-line basis over the lease term. The amortization of the lease asset is calculated as the straight-line lease expense less the accretion of the interest on the lease liability each period. The lease liability is reduced by the cash payment less the interest each period.