Employee Savings Plan	12 Months Ended
Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Savings Plan	Employee Savings Plan For the first ten months of 2018, under the Company’s Employee Savings Plan, a defined contribution plan, U.S. employees, who had attained age 21 and were not defined as highly compensated, could have contributed up to 50% of their pay on a pre-tax basis subject to the annual dollar limitations established by the Internal Revenue Service (IRS). Highly compensated employees as defined by the IRS, could have contributed up to 25% of their pay on a pre-tax basis. The Company matched 50% of the first 6% of pay an employee contributed. Company contributions vested 20%, 40%, 60%, and 100% after two, three, four, and five years of continuous employment with the Company, respectively. On November 1, 2018, the Company changed the custodian of the Employee Savings Plan which altered the contribution rate and vesting period. Commencing on that date, all U.S. employees, whether they are determined to be highly compensated or not, who have attained age 21 may contribute up to 100% of their pay on a pre-tax basis under the Company's Employee Savings Plan. The Company still matches 50% of the first 6% of pay an employee contributes. Company contributions vest 25%, 50%, 75%, and 100% after one, two, three, and four years of continuous employment with the Company, respectively. Company contributions totaled $2,540,000 in 2018, $2,030,000 in 2017, and $1,712,000 in 2016. Cognex stock is not an investment alternative and Company contributions are not made in the form of Cognex stock.

Employee Savings Plan

For the first ten months of 2018, under the Company’s Employee Savings Plan, a defined contribution plan, U.S. employees, who had attained age 21 and were not defined as highly compensated, could have contributed up to 50% of their pay on a pre-tax basis subject to the annual dollar limitations established by the Internal Revenue Service (IRS). Highly compensated employees as defined by the IRS, could have contributed up to 25% of their pay on a pre-tax basis. The Company matched 50% of the first 6% of pay an employee contributed. Company contributions vested 20%, 40%, 60%, and 100% after two, three, four, and five years of continuous employment with the Company, respectively.

On November 1, 2018, the Company changed the custodian of the Employee Savings Plan which altered the contribution rate and vesting period. Commencing on that date, all U.S. employees, whether they are determined to be highly compensated or not, who have attained age 21 may contribute up to 100% of their pay on a pre-tax basis under the Company's Employee Savings Plan. The Company still matches 50% of the first 6% of pay an employee contributes. Company contributions vest 25%, 50%, 75%, and 100% after one, two, three, and four years of continuous employment with the Company, respectively. Company contributions totaled $2,540,000 in 2018, $2,030,000 in 2017, and $1,712,000 in 2016. Cognex stock is not an investment alternative and Company contributions are not made in the form of Cognex stock.