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Commitments and Contingencies (Details Textual) (USD $) In Millions, unless otherwise specified | Sep. 30, 2014
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Commitments and Contingencies (Textual) [Abstract] |
Rental payment obligations during the remaining terms of these leases | $ 3.2

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

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- Definition Total lease obligation for the period when the Company is the guarantor on a lease, sublets and becomes the secondary guarantor. + References No definition available. + Details
Name: | gpi_SecondaryGuarantorLeaseObligations
Namespace Prefix: | gpi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant