Cash, Cash Equivalents, and Investments - Summary of Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 05, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 509,924
Gross Unrealized Gains	1,027
Gross Unrealized Losses	(131)
Fair Value	510,820us-gaap_AvailableForSaleSecurities
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(110)
Corporate Bonds \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,356
Gross Unrealized Gains	58
Gross Unrealized Losses	(1)
Fair Value	37,413
Corporate Bonds \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	203,712
Gross Unrealized Gains	618
Gross Unrealized Losses	(109)
Fair Value	204,221
Supranational bonds \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,900
Gross Unrealized Gains	2
Gross Unrealized Losses	0
Fair Value	1,902
Euro liquidity fund \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,866
Gross Unrealized Gains	179
Gross Unrealized Losses	0
Fair Value	62,045
Municipal Bonds \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,814
Gross Unrealized Gains	5
Gross Unrealized Losses	0
Fair Value	1,819
Municipal Bonds \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,855
Gross Unrealized Gains	25
Gross Unrealized Losses	0
Fair Value	4,880
Sovereign Bonds \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,594
Gross Unrealized Gains	11
Gross Unrealized Losses	0
Fair Value	5,605
Sovereign Bonds \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,033
Gross Unrealized Gains	7
Gross Unrealized Losses	0
Fair Value	6,040
Asset-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(12)
Asset-Backed Securities \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	392
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	392
Asset-Backed Securities \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	77,417
Gross Unrealized Gains	43
Gross Unrealized Losses	(12)
Fair Value	77,448
Treasury Bills
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Losses	(9)
Treasury Bills \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,652
Gross Unrealized Gains	0
Gross Unrealized Losses	(8)
Fair Value	31,644
Treasury Bills \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,468
Gross Unrealized Gains	57
Gross Unrealized Losses	(1)
Fair Value	64,524
Agency Bonds \| Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,521
Gross Unrealized Gains	2
Gross Unrealized Losses	0
Fair Value	1,523
Agency Bonds \| Long-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,344
Gross Unrealized Gains	20
Gross Unrealized Losses	0
Fair Value	$ 11,364

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

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

- Definition

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

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

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

+ Details

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

- Details

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

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cgnx_AgencyBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cgnx_EuroliquidityfundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=cgnx_SupranationalbondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_SovereignDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: