Taxes - Constituents of Deferred Tax Assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current deferred tax assets:
Inventory and revenue related	$ 4,911us-gaap_DeferredTaxAssetsInventory	$ 5,614us-gaap_DeferredTaxAssetsInventory
Bonuses, commissions, and other compensation	2,280	1,377
Other	1,794cgnx_DeferredTaxAssetsOtherCurrent	1,292cgnx_DeferredTaxAssetsOtherCurrent
Gross current deferred tax assets	8,985us-gaap_DeferredTaxAssetsGrossCurrent	8,283us-gaap_DeferredTaxAssetsGrossCurrent
Valuation allowance	0	(672)
Net current deferred tax assets	8,985us-gaap_DeferredTaxAssetsNetCurrent	7,611us-gaap_DeferredTaxAssetsNetCurrent
Noncurrent deferred tax assets:
Stock-based compensation expense	10,290	7,488
Federal and state tax credit carryforwards	4,547	5,418
Depreciation	1,945	1,831
Acquired completed technologies and other intangible assets	450cgnx_DeferredTaxAssetsIntangibles	835cgnx_DeferredTaxAssetsIntangibles
Unrealized investment gains and losses	355	601
Correlative tax relief and deferred interest related to reserves	342	252
Other	1,436cgnx_DeferredTaxAssetsOtherNoncurrent	1,178cgnx_DeferredTaxAssetsOtherNoncurrent
Gross noncurrent deferred tax assets	19,365	17,603
Noncurrent deferred tax liabilities:
Nondeductible intangible assets	(2,430)	(3,662)
Other	0us-gaap_DeferredTaxLiabilitiesOther	(548)us-gaap_DeferredTaxLiabilitiesOther
Gross noncurrent deferred tax liabilities	(2,430)	(4,210)
Valuation allowance	(2,483)	(1,086)
Net noncurrent deferred tax assets	$ 14,452	$ 12,307

Deferred tax assets intangibles.

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Deferred tax assets other current.

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Deferred tax assets other non current.

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Deferred tax assets tax credit carry forwards foreign and state.

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Deferred tax assets unrealized investment gains and losses.

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Noncurrent deferred tax assets deprecation.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from inventory.

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Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards, net of deferred tax liability attributable to taxable temporary differences expected to be realized or consumed after one year (or the normal operating cycle, if longer).

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from other compensation and benefits not separately disclosed.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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Amount of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized expected to be realized or consumed after one year (or the normal operating cycle, if longer).

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Amount of deferred tax liability attributable to taxable temporary differences from intangible assets other than goodwill.

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