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Commitments and Contingencies (Details Textual) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Mar. 31, 2017 dealerships
Manufacturer [Line Items]
Proceeds from Legal Settlements	$ 13.2
Volkswagen legal claims	$ 14,700.0
Volkswagen [Member]
Manufacturer [Line Items]
Number Of Dealerships | dealerships		7

X

- Definition

[Line Items] for Manufacturer [Table]

+ References

No definition available.

+ Details

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Namespace Prefix:	gpi_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

Number of dealerships.

+ References

No definition available.

+ Details

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Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
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X

- Definition

Volkswagen legal claims

+ References

No definition available.

+ Details

Name:	gpi_Volkswagenlegalclaims
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Cash received for the settlement of litigation during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585

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- Details

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