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Operating Leases (Details Textual) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Leases [Abstract] |  |  |
Total term of lease facility | 30 years |  |
Initial term of lease facilities | 15 years |  |
Number of additional extensions on lease facility | 3 gpi_Numberofadditionalextensionsonleasefacility |  |
Operating Leases (Textual) [Abstract] |  |  |
Extended period of lease under option | 5 years |  |
Future, non-cancelable sublease payments | $ 2.4 us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals |  |
Total rent expense under all operating leases | $ 58.9 us-gaap_OperatingLeasesRentExpenseNet | $ 59.7 us-gaap_OperatingLeasesRentExpenseNet | $ 50.4 us-gaap_OperatingLeasesRentExpenseNet

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- Definition Extended period of lease under option. + References No definition available. + Details
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- Definition Initial term of lease facilities + References No definition available. + Details
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Namespace Prefix: | gpi_
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- Definition Number of additional extensions on lease facility + References No definition available. + Details
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Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Definition Total term of lease facility + References No definition available. + Details
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- Details
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- Definition Contractually required future rental payments receivable on noncancelable subleasing arrangements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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- Definition Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717 + Details
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