Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Apr. 04, 2015	Jan. 03, 2015
Short-term investments:
Available-for-sale securities	$ 92,640us-gaap_AvailableForSaleSecurities	$ 90,445us-gaap_AvailableForSaleSecurities
Trading securities held in Non-Qualified Deferred Compensation plan, or NQDC	23,365us-gaap_DeferredCompensationPlanAssets	27,034us-gaap_DeferredCompensationPlanAssets
2015 Notes Hedges	429,847	523,930
Foreign currency exchange contracts	3,081
Total Assets	1,227,359us-gaap_AssetsFairValueDisclosure	1,369,905us-gaap_AssetsFairValueDisclosure
Liabilities
2015 Notes Embedded Conversion Derivative	429,847	523,930
Foreign currency exchange contracts		3,163
Total Liabilities	429,847us-gaap_LiabilitiesFairValueDisclosure	527,093us-gaap_LiabilitiesFairValueDisclosure
Money market funds [Member]
Assets
Cash equivalents	678,426	728,496
Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities	33,521	34,894
Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities	18,307	21,910
United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities	26,629	19,374
United States government agency securities [Member]
Short-term investments:
Available-for-sale securities	8,160	9,208
Commercial paper [Member]
Short-term investments:
Available-for-sale securities	4,199	3,186
Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	1,824	1,873
Fair Value Measurements, Level 1 [Member]
Short-term investments:
Trading securities held in Non-Qualified Deferred Compensation plan, or NQDC	23,365	27,034
2015 Notes Hedges	0	0
Foreign currency exchange contracts	0
Total Assets	738,404	785,985
Liabilities
2015 Notes Embedded Conversion Derivative	0	0
Foreign currency exchange contracts		0
Total Liabilities	0	0
Fair Value Measurements, Level 1 [Member] \| Money market funds [Member]
Assets
Cash equivalents	678,426	728,496
Fair Value Measurements, Level 1 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 1 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 1 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities	26,629	19,374
Fair Value Measurements, Level 1 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities	8,160	9,208
Fair Value Measurements, Level 1 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 1 [Member] \| Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	1,824	1,873
Fair Value Measurements, Level 2 [Member]
Short-term investments:
Trading securities held in Non-Qualified Deferred Compensation plan, or NQDC	0	0
2015 Notes Hedges	429,847	523,930
Foreign currency exchange contracts	3,081
Total Assets	488,955	583,920
Liabilities
2015 Notes Embedded Conversion Derivative	429,847	523,930
Foreign currency exchange contracts		3,163
Total Liabilities	429,847	527,093
Fair Value Measurements, Level 2 [Member] \| Money market funds [Member]
Assets
Cash equivalents	0	0
Fair Value Measurements, Level 2 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities	33,521	34,894
Fair Value Measurements, Level 2 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities	18,307	21,910
Fair Value Measurements, Level 2 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 2 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 2 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities	4,199	3,186
Fair Value Measurements, Level 2 [Member] \| Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member]
Short-term investments:
Trading securities held in Non-Qualified Deferred Compensation plan, or NQDC	0	0
2015 Notes Hedges	0	0
Foreign currency exchange contracts	0
Total Assets	0	0
Liabilities
2015 Notes Embedded Conversion Derivative	0	0
Foreign currency exchange contracts		0
Total Liabilities	0	0
Fair Value Measurements, Level 3 [Member] \| Money market funds [Member]
Assets
Cash equivalents	0	0
Fair Value Measurements, Level 3 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities	0	0
Fair Value Measurements, Level 3 [Member] \| Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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

- Details

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

- 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=28360136&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=6871852&loc=d3e26610-111562

+ Details

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

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

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

- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ 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 210.5-02.17)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226000-175313

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

+ Details

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

- Definition

Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

+ References

No definition available.

+ Details

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

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByAssetClassAxis=cdns_MarketableEquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: