Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Apr. 05, 2015	Mar. 30, 2014
Revenue
Product	$ 105,775us-gaap_SalesRevenueGoodsNet	$ 83,569us-gaap_SalesRevenueGoodsNet
Service	7,659us-gaap_SalesRevenueServicesNet	7,360us-gaap_SalesRevenueServicesNet
Total revenue	113,434us-gaap_SalesRevenueNet	90,929us-gaap_SalesRevenueNet
Cost of revenue
Product	23,634us-gaap_CostOfGoodsSold	17,286us-gaap_CostOfGoodsSold
Service	4,320us-gaap_CostOfServices	3,798us-gaap_CostOfServices
Total cost of revenue	27,954us-gaap_CostOfGoodsAndServicesSold	21,084us-gaap_CostOfGoodsAndServicesSold
Gross margin
Product	82,141cgnx_GrossMarginProducts	66,283cgnx_GrossMarginProducts
Service	3,339cgnx_GrossMarginServices	3,562cgnx_GrossMarginServices
Total gross margin	85,480us-gaap_GrossProfit	69,845us-gaap_GrossProfit
Research, development, and engineering expenses	18,076us-gaap_ResearchAndDevelopmentExpense	12,502us-gaap_ResearchAndDevelopmentExpense
Selling, general, and administrative expenses	43,487	34,900
Operating income	23,917us-gaap_OperatingIncomeLoss	22,443us-gaap_OperatingIncomeLoss
Foreign currency gain (loss)	405	(110)
Investment income	850us-gaap_InvestmentIncomeNonoperating	787us-gaap_InvestmentIncomeNonoperating
Other expense	(310)us-gaap_OtherNonoperatingIncomeExpense	(273)us-gaap_OtherNonoperatingIncomeExpense
Income before income tax expense	24,862	22,847
Income tax expense	4,360us-gaap_IncomeTaxExpenseBenefit	4,341us-gaap_IncomeTaxExpenseBenefit
Net income	$ 20,502us-gaap_NetIncomeLoss	$ 18,506us-gaap_NetIncomeLoss
Earnings per weighted-average common and common-equivalent share:
Basic (in dollars per share)	$ 0.24us-gaap_EarningsPerShareBasic	$ 0.21us-gaap_EarningsPerShareBasic
Diluted (in dollars per share)	$ 0.23us-gaap_EarningsPerShareDiluted	$ 0.21us-gaap_EarningsPerShareDiluted
Weighted-average common and common-equivalent shares outstanding:
Basic (in shares)	86,764	86,879
Diluted (in shares)	88,749	89,259

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