Stock-Based Compensation Expense (Detail)	3 Months Ended	9 Months Ended
Oct. 04, 2015 USD ($) group $ / shares shares	Sep. 28, 2014 USD ($) $ / shares	Oct. 04, 2015 USD ($) group $ / shares shares	Sep. 28, 2014 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	1.25%	0.00%	1.25%	0.00%
Groups within the employee population \| group	2		2
Percentage of stock options granted to senior management	74.00%		74.00%
Percentage of stock options granted to all other employees	73.00%		73.00%
Estimated annual forfeiture rate	10.00%		10.00%
Estimated annual forfeiture rate for unvested options	11.00%		11.00%
Increase (decrease) to compensation expense	$ 461,000	$ 288,000
Weighted-average grant-date fair values, in dollars per share \| $ / shares	$ 14.36	$ 15.45	$ 14.35	$ 15.35
Total intrinsic value	$ 4,506,000	$ 14,461,000	$ 43,737,000	$ 29,104,000
Total fair values of stock options vest	565,000	268,000	14,984,000	11,251,000
Unrecognized compensation expense	22,169,000		$ 22,169,000
Weighted average period to be recognized			1 year 8 months 16 days
Stock-based compensation expense	5,493,000	3,298,000	$ 17,070,000	11,258,000
Tax benefit from compensation expense	1,865,000	$ 1,098,000	5,734,000	$ 3,670,000
Recognized period costs capitalized	$ 0		$ 0
Vesting period, performance-based restricted stock, years			1 year
Vesting period, time-based restricted stock, years			3 years
General Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for stock option plans			4 years
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant under stock option plans \| shares	7,817,714		7,817,714
Expiration period from grant day			10 years
Discontinued Operations, Disposed of by Sale
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accelerated vesting of stock options, shares \| shares	190,000		190,000
Stock-based compensation expense	$ 1,106,000

Employee service share based compensation recognized period costs capitalized amount.

No definition available.

Name:	cgnx_EmployeeServiceShareBasedCompensationRecognizedPeriodCostsCapitalizedAmount
Namespace Prefix:	cgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Period for Recognition

+ References

No definition available.

+ Details

Name:	cgnx_EmployeeServiceSharebasedCompensationNonvestedAwardsCompensationNotyetRecognizedPeriodforRecognition
Namespace Prefix:	cgnx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimated forfeiture rate for unvested options for all non-senior management.

+ References

No definition available.

+ Details

Name:	cgnx_EstimatedForfeitureRateForUnvestedOptionsForAllNonSeniorManagement
Namespace Prefix:	cgnx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Estimated forfeiture rate for unvested options for senior management.

+ References

No definition available.

+ Details

Name:	cgnx_EstimatedForfeitureRateForUnvestedOptionsForSeniorManagement
Namespace Prefix:	cgnx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Expiration period of stock option plan.

+ References

No definition available.

+ Details

Name:	cgnx_ExpirationPeriodOfStockOptionPlan
Namespace Prefix:	cgnx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase (decrease) in compensation expense due to revised estimated forfeiture rates.

+ References

No definition available.

+ Details

Name:	cgnx_IncreaseInCompensationExpenseDueToRevisedEstimatedForfeitureRates
Namespace Prefix:	cgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of groups within employee population.

+ References

No definition available.

+ Details

Name:	cgnx_NumberOfGroupsWithinEmployeePopulation
Namespace Prefix:	cgnx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of stock options granted to all other employees expected to vest.

+ References

No definition available.

+ Details

Name:	cgnx_PercentageOfStockOptionsGrantedToAllOtherEmployeesExpectedToVest
Namespace Prefix:	cgnx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of stock options granted to senior management expected to vest.

+ References

No definition available.

+ Details

Name:	cgnx_PercentageOfStockOptionsGrantedToSeniorManagementExpectedToVest
Namespace Prefix:	cgnx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment award options vested fair value.

+ References

No definition available.

+ Details

Name:	cgnx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedFairValue
Namespace Prefix:	cgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Shares based compensation arrangement by shares based payment award options exercisable intrinsic value.

+ References

No definition available.

+ Details

Name:	cgnx_SharesBasedCompensationArrangementBySharesBasedPaymentAwardOptionsExercisableIntrinsicValue
Namespace Prefix:	cgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Vesting period, performance-based restricted stock, years

+ References

No definition available.

+ Details

Name:	cgnx_Vestingperiodperformancebasedrestrictedstockyears
Namespace Prefix:	cgnx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Vesting period, time-based restricted stock, years

+ References

No definition available.

+ Details

Name:	cgnx_Vestingperiodtimebasedrestrictedstockyears
Namespace Prefix:	cgnx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(iii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PlanNameAxis=cgnx_GeneralStockOptionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: