Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Jan. 02, 2016
Short-term investments:
Available-for-sale securities		$ 94,498
Trading securities held in Non-Qualified Deferred Compensation Plan, or NQDC	$ 26,622	24,905
Total Assets	267,403	480,094
Liabilities
Foreign currency exchange contracts	2,653	362
Money market funds [Member]
Assets
Money market funds	237,724	360,691
Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities		34,829
Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities		15,046
United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities		36,286
United States government agency securities [Member]
Short-term investments:
Available-for-sale securities		4,152
Commercial paper [Member]
Short-term investments:
Available-for-sale securities		1,993
Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	3,057	2,192
Fair Value Measurements, Level 1 [Member]
Short-term investments:
Trading securities held in Non-Qualified Deferred Compensation Plan, or NQDC	26,622	24,905
Total Assets	267,403	428,226
Liabilities
Foreign currency exchange contracts	0	0
Fair Value Measurements, Level 1 [Member] \| Money market funds [Member]
Assets
Money market funds	237,724	360,691
Fair Value Measurements, Level 1 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 1 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 1 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities		36,286
Fair Value Measurements, Level 1 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities		4,152
Fair Value Measurements, Level 1 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 1 [Member] \| Marketable equity securities [Member]
Short-term investments:
Available-for-sale securities	3,057	2,192
Fair Value Measurements, Level 2 [Member]
Short-term investments:
Trading securities held in Non-Qualified Deferred Compensation Plan, or NQDC	0	0
Total Assets	0	51,868
Liabilities
Foreign currency exchange contracts	2,653	362
Fair Value Measurements, Level 2 [Member] \| Money market funds [Member]
Assets
Money market funds	0	0
Fair Value Measurements, Level 2 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities		34,829
Fair Value Measurements, Level 2 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities		15,046
Fair Value Measurements, Level 2 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 2 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 2 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities		1,993
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
Total Assets	0	0
Liabilities
Foreign currency exchange contracts	0	0
Fair Value Measurements, Level 3 [Member] \| Money market funds [Member]
Assets
Money market funds	0	0
Fair Value Measurements, Level 3 [Member] \| Corporate debt securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 3 [Member] \| Bank certificates of deposit [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 3 [Member] \| United States Treasury securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 3 [Member] \| United States government agency securities [Member]
Short-term investments:
Available-for-sale securities		0
Fair Value Measurements, Level 3 [Member] \| Commercial paper [Member]
Short-term investments:
Available-for-sale securities		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=66048111&loc=d3e19207-110258

+ Details

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

- References

No definition available.

+ 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=65884222&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=73527792&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=66010992&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

+ Details

Name:	us-gaap_DeferredCompensationPlanAssets
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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_MoneyMarketFundsMember
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_CertificatesOfDepositMember
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_FairValueByAssetClassAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
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=cdns_MarketableEquitySecuritiesMember
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: