Inventories, Contracts in Progress and Vehicle Floor Plan Payable (Narrative) (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Inventory [Line Items]
Weighted average interest rate	5.00%	5.10%
Automotive [Member]
Inventory [Line Items]
Borrowing capacity	$ 50,000,000
Vehicle floor plan payable	28,400,000
Floor plan assistance	$ 600,000	$ 400,000
Automotive [Member] \| Vehicle Floor Plan Facility [Member]
Inventory [Line Items]
Weighted average interest rate	1.20%	2.60%
London Interbank Offered Rate (LIBOR) [Member] \| Automotive [Member] \| Vehicle Floor Plan Facility [Member]
Inventory [Line Items]
Applicable interest rate margin	1.15%

The amount of assistance received from the manufacturers recognized as a reduction of operating expenses.

No definition available.

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Namespace Prefix:	ghc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate borrowing capacity under the vehicle floor plan facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facilities.

+ References

No definition available.

+ Details

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

- Definition

The amount borrowed to finance the purchase of specific vehicle inventories.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The average effective interest rate during the reporting period.

+ 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
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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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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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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