Cash, Cash Equivalents and Investments - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cash balance included foreign bank balance	$ 43,732,000cgnx_DueFromForeignBanks	$ 32,096,000cgnx_DueFromForeignBanks
Gross realized gains on sale of debt securities	843,000	508,000	1,990,000
Gross realized losses on sale of debt securities	170,000	194,000	295,000
Maximum amount committed to invest in limited partnership	20,500,000
Contribution to limited partnership	19,886,000cgnx_ContributionToLimitedPartnership
Remaining amount of commitment in limited partnership	614,000cgnx_RemainingAmountOfCommitment
Received a stock distribution		362,000	2,193,000
Proceeds for liquidation of stock		347,000	2,128,000
Recorded a realized loss on stock distribution		15,000	65,000
Proceeds from Limited Partnership Investments		1,422,000
Carrying value of investment	1,956,000us-gaap_CostMethodInvestments	1,956,000us-gaap_CostMethodInvestments
Cost Method Investments, Fair Value Disclosure	6,200,000
Payments to Acquire Marketable Securities			2,136,000
Trading Securities, Unrealized Holding Loss			5,000
Trading Securities		1,429,000us-gaap_TradingSecurities
Trading Securities, Realized Loss		$ 702,000us-gaap_TradingSecuritiesRealizedLoss

Contribution to limited partnership.

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Due from foreign banks.

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Maximum amount committed to invest in limited partnership.

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Proceeds From Sale Of Cost Method Investment

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Remaining amount of commitment in limited partnership.

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Stock distribution received from limited partnership company.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

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Fair value portion of investments accounted under the cost method.

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For investments in debt and equity securities accounted for at cost, the excess of the carrying amount over net sale proceeds of investments disposed of during the period.

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Cash outflow for purchase of trading, available-for-sale securities and held-to-maturity securities.

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Cash inflow received as distributions, returns of capital, or sale proceeds from partnership interests held for investment purposes.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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Amount of unrealized holding loss before gain recognized in the income statement for investments in trading securities.

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