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Annual Financial Information (Details Textual)	Dec. 31, 2014
Business and Organization [Line Items]
Number of international regions	2gpi_Numberofinternationalregions
East [Member]
Business and Organization [Line Items]
Number of dealerships	41gpi_NumberOfDealerships / us-gaap_StatementGeographicalAxis = gpi_EastMember
West [Member]
Business and Organization [Line Items]
Number of dealerships	75gpi_NumberOfDealerships / us-gaap_StatementGeographicalAxis = gpi_WestMember
UNITED STATES
Business and Organization [Line Items]
Number of States in which Entity Operates	14us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_StatementGeographicalAxis = country_US
UNITED KINGDOM
Business and Organization [Line Items]
Number of Towns in which Entity Operates	16gpi_NumberOfTownsInWhichEntityOperates / us-gaap_StatementGeographicalAxis = country_GB
Number of dealerships	17gpi_NumberOfDealerships / us-gaap_StatementGeographicalAxis = country_GB
BRAZIL
Business and Organization [Line Items]
Number of States in which Entity Operates	3us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_StatementGeographicalAxis = country_BR
Number of dealerships	17gpi_NumberOfDealerships / us-gaap_StatementGeographicalAxis = country_BR

X

- Details

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Namespace Prefix:	gpi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of dealerships.

+ References

No definition available.

+ Details

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Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of international regions

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of Towns in which Entity Operates

+ References

No definition available.

+ Details

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Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

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- Details

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Period Type:

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- Details

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

X

- Details

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

X

- Details

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

X

- Details

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Namespace Prefix:
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Period Type: