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Intangible Franchise Rights and Goodwill (Details Textual) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Countries and States [Line Items] |  |  |
Accumulated Impairments | 42.4 gpi_AccumulatedImpairments |  |
Intangible Franchise Rights and Goodwill (Textual) [Abstract] |  |  |
Number Of Dealerships Acquired |  |  | 16 gpi_NumberOfDealershipsAcquired
UNITED STATES |  |  |
Intangible Franchise Rights and Goodwill (Textual) [Abstract] |  |  |
Number Of Dealerships Acquired | 7 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_US | 9 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_US | 10 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_US
BRAZIL |  |  |
Intangible Franchise Rights and Goodwill (Textual) [Abstract] |  |  |
Number Of Dealerships Acquired | 1 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_BR | 18 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_BR |
UNITED KINGDOM |  |  |
Intangible Franchise Rights and Goodwill (Textual) [Abstract] |  |  |
Number Of Dealerships Acquired | 3 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_GB | 4 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_GB | 6 gpi_NumberOfDealershipsAcquired / gpi_CountriesAndStatesAxis = country_GB

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- Definition Accumulated impairments. + References No definition available. + Details
Name: | gpi_AccumulatedImpairments
Namespace Prefix: | gpi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | gpi_CountriesAndStatesLineItems
Namespace Prefix: | gpi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | gpi_IntangibleFranchiseRightsAndGoodwillTextualAbstract
Namespace Prefix: | gpi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of dealerships acquired. + References No definition available. + Details
Name: | gpi_NumberOfDealershipsAcquired
Namespace Prefix: | gpi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | gpi_CountriesAndStatesAxis=country_BR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | gpi_CountriesAndStatesAxis=country_GB
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | gpi_CountriesAndStatesAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |