Revenue (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) business
Disaggregation of Revenue [Line Items]
Deferred revenue recognized in period related to beginning balance \| $	$ 159.3
Maximum Term of Contract	1 year
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue	81.00%
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue	19.00%
Non-U.S. [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue	26.00%
U.S. [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue	74.00%
Higher Education [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations	1
Test Preparation [Member]
Disaggregation of Revenue [Line Items]
Minimum Term of Contract	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Test Preparation [Member] \| Long-term Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Revenue, Remaining Performance Obligation \| $	$ 7.0
Revenue Remaining Performance Obligation Percentage of Revenue Expected to be Recognized Over Next 12 Months	80.00%
Kaplan International [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations	1
Number of Business Lines \| business	1
Manufacturing [Member]
Disaggregation of Revenue [Line Items]
Number of Business Lines \| business	4
Revenue Recognition, Maximum Period between Recognition of Revenue and Receipt of Payment	90 days
Manufacturing [Member] \| Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Percentage of Revenue	29.00%
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
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
Advertising Revenue [Member] \| Television Broadcasting [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
Retransmission Revenue [Member] \| Television Broadcasting [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
Other Healthcare Services [Member] \| Healthcare [Member]
Disaggregation of Revenue [Line Items]
Number of Performance Obligations	1

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

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

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response))
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

+ 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130556-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

+ Details

Name:	us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ghc_HigherEducationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_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:	us-gaap_ProductOrServiceAxis=ghc_KaplanInternationalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ghc_ManufacturingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ghc_HealthcareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ghc_SocialCodeMember
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:	us-gaap_ProductOrServiceAxis=ghc_TelevisionBroadcastingMember
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:	ghc_RevenueSourceAxis=ghc_OtherHealthcareServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: