Debt (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019	Oct. 09, 2014
Debt Instrument [Line Items]
Principal	$ 700,000	$ 350,000
Unamortized Discount	(3,416)	(3,981)
Carrying Value	350,000	0
Carrying Value	346,584	346,019
Carrying Value	696,584	346,019
Senior Notes [Member] \| Senior Notes Due 2024 [Member]
Debt Instrument [Line Items]
Principal	350,000	350,000	$ 350,000
Unamortized Discount	(3,416)	(3,981)	$ (1,400)
Carrying Value	346,584	346,019
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal	350,000	0
Carrying Value	$ 350,000	$ 0

Carrying Value Of Debt Outstanding

No definition available.

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Namespace Prefix:	cdns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Principal Amount Oustanding Of Revolving Line of Credit

+ References

No definition available.

+ Details

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Namespace Prefix:	cdns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Remaining Principal Amount Of Debt Outstanding

+ References

No definition available.

+ Details

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Namespace Prefix:	cdns_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
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+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
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+ Details

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- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

+ References

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-Publisher FASB
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-SubTopic 10
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+ Details

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- Details

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- Details

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- Details

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