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Commitments and Contingencies - (Details) $ in Millions | Dec. 31, 2018 USD ($)
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Commitments and Contingencies Disclosure [Abstract] |
Lessee rental payment obligations during remaining terms of leases under guarantee agreement | $ 42.1

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- Definition Guarantor Obligations, Maximum Exposure Inestimable, Minimum Lease Payments Guaranteed + References No definition available. + Details
Name: | gpi_GuarantorObligationsMaximumExposureInestimableMinimumLeasePaymentsGuaranteed
Namespace Prefix: | gpi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration