Maximum Term of Contract

No definition available.

Name:	ghc_MaximumTermofContract
Namespace Prefix:	ghc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum Term of Contract

+ References

No definition available.

+ Details

Name:	ghc_MinimumTermofContract
Namespace Prefix:	ghc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of business lines.

+ References

No definition available.

+ Details

Name:	ghc_NumberofBusinessLines
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Performance Obligations in standard contract

+ References

No definition available.

+ Details

Name:	ghc_NumberofPerformanceObligations
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Performance Obligations In Contract With Tuition Cap

+ References

No definition available.

+ Details

Name:	ghc_NumberofPerformanceObligationsInContractWithTuitionCap
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of Revenue Recognized During Period from Contract with Customer, Excluding Assessed Tax

+ References

No definition available.

+ Details

Name:	ghc_PercentageofRevenuefromContractwithCustomerExcludingAssessedTax
Namespace Prefix:	ghc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment

+ References

No definition available.

+ Details

Name:	ghc_RevenueRecognitionMaximumPeriodbetweenRecognitionofRevenueandReceiptofPayment
Namespace Prefix:	ghc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue Remaining Performance Obligation Percentage of Revenue Expected to be Recognized Over Next 12 Months

+ References

No definition available.

+ Details

Name:	ghc_RevenueRemainingPerformanceObligationPercentageofRevenueExpectedtobeRecognizedOverNext12Months
Namespace Prefix:	ghc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Transition and Operations Support Agreement Initial Term

+ References

No definition available.

+ Details

Name:	ghc_TransitionandOperationsSupportAgreementInitialTerm
Namespace Prefix:	ghc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

Name:	us-gaap_CapitalizedContractCostAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue recognized that was previously reported as deferred or unearned revenue.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredRevenueRevenueRecognized1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

+ Details

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

- Definition

Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

+ Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_ProductOrServiceAxis=ghc_KaplanInternationalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ghc_HigherEducationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ghc_TestPreparationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ContractWithCustomerDurationAxis=us-gaap_LongTermContractWithCustomerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ghc_TelevisionBroadcastingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_RevenueSourceAxis=ghc_AdvertisingRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_RevenueSourceAxis=ghc_RetransmissionRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ghc_ManufacturingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_HealthCareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_RevenueSourceAxis=ghc_OtherHealthcareServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=ghc_SocialCodeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TimingOfTransferOfGoodOrServiceAxis=us-gaap_TransferredOverTimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TimingOfTransferOfGoodOrServiceAxis=us-gaap_TransferredAtPointInTimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=us-gaap_NonUsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Revenue (Narrative) (Details) $ in Thousands		3 Months Ended			9 Months Ended
Revenue (Narrative) (Details) $ in Thousands	Mar. 22, 2018	Sep. 30, 2018 USD ($) business	Mar. 31, 2018	Mar. 22, 2018	Sep. 30, 2018 USD ($) business
Disaggregation of Revenue [Line Items]
Maximum Term of Contract					1 year
Deferred revenue recognized in period related to beginning balance					$ 239,600
Costs amortized during the period		$ 10,900			$ (33,642)
Kaplan International [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
Number of Business Lines \| business		1			1
Higher Education [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations			1	1
Number of Performance Obligations In Contract With Tuition Cap			2
Transition and Operations Support Agreement Initial Term	30 years
Test Preparation [Member] \| Long-term Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation, Amount		$ 6,200			$ 6,200
Revenue Remaining Performance Obligation Percentage of Revenue Expected to be Recognized Over Next 12 Months		82.00%			82.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		12 months			12 months
Minimum Term of Contract					12 months
Television Broadcasting [Member] \| Advertising Revenue [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment					60 days
Television Broadcasting [Member] \| Retransmission Revenue [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment					60 days
Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment					90 days
Number of Business Lines \| business		4			4
Healthcare [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment					60 days
Healthcare [Member] \| Other Healthcare Services [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
SocialCode [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations					1
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment					45 days
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue		80.00%			80.00%
Transferred over Time [Member] \| Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue		25.00%			27.00%
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue		20.00%			20.00%
U.S. [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue		78.00%			76.00%
Non-US [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue		22.00%			24.00%