Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	$ 717,043	$ 431,916
Gross Unrealized Gains	411	143
Gross Unrealized Losses	(120)	(78)
Debt Securities, Available-for-sale	717,334	431,981
Cash equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	137,783	249,952
Debt Securities, Available-for-sale	137,783	249,952
Cash equivalents [Member] \| Money market funds [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	40,027	185,666
Debt Securities, Available-for-sale	40,027	185,666
Cash equivalents [Member] \| Time deposits [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	36,756	64,286
Debt Securities, Available-for-sale	36,756	64,286
Cash equivalents [Member] \| Commercial paper [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	61,000
Debt Securities, Available-for-sale	61,000
Short-term investments [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	442,277	85,778
Gross Unrealized Gains	259	52
Gross Unrealized Losses	(63)	(11)
Debt Securities, Available-for-sale	442,473	85,819
Short-term investments [Member] \| Time deposits [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	28,302	2,506
Debt Securities, Available-for-sale	28,302	2,506
Short-term investments [Member] \| Commercial paper [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	264,000
Gross Unrealized Gains	12
Gross Unrealized Losses	(19)
Debt Securities, Available-for-sale	263,993
Short-term investments [Member] \| Government and corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	149,975	83,272
Gross Unrealized Gains	247	52
Gross Unrealized Losses	(44)	(11)
Debt Securities, Available-for-sale	150,178	83,313
Long-term investments [Member] \| Government and corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost	136,983	96,186
Gross Unrealized Gains	152	91
Gross Unrealized Losses	(57)	(67)
Debt Securities, Available-for-sale	$ 137,078	$ 96,210

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

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

- 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

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_BankTimeDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cern_GovernmentAndCorporateBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=cern_LongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: