Other Income, Net (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Jan. 03, 2015	Dec. 28, 2013	Dec. 29, 2012
Other Income (Expense), Net
Interest income	$ 1,827us-gaap_InvestmentIncomeInterest	$ 1,706us-gaap_InvestmentIncomeInterest	$ 1,473us-gaap_InvestmentIncomeInterest
Gains on sale of marketable debt and equity securities, net	722	1,364	141
Gains on sale of non-marketable equity investments	2,524us-gaap_RealizedInvestmentGainsLosses	1,098us-gaap_RealizedInvestmentGainsLosses	2,830us-gaap_RealizedInvestmentGainsLosses
Gains on securities in NQDC trust	3,415	3,293	4,453
Gains on foreign exchange	1,742	285	3,263
Write-down of non-marketable investments	(1,956)us-gaap_ImpairmentOfInvestments	(464)us-gaap_ImpairmentOfInvestments	(1,103)us-gaap_ImpairmentOfInvestments
Other income, net	205cdns_OtherIncomeExpense	288cdns_OtherIncomeExpense	284cdns_OtherIncomeExpense
Total other income, net	$ 8,479us-gaap_OtherNonoperatingIncomeExpense	$ 7,570us-gaap_OtherNonoperatingIncomeExpense	$ 11,341us-gaap_OtherNonoperatingIncomeExpense

Gains (losses) on trading securities in the non-qualified deferred compensation trust.

No definition available.

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- Definition

Aggregate of other income (expense) items not separately disclosed.

+ References

No definition available.

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- Definition

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 1

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

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-SubTopic 10

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- Definition

Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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This item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as trading, available-for-sale, or held-to-maturity. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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