Revenue Recognition, Multiple-deliverable Arrangements [Table] (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
New Vehicle Retail Sales	$ 1,513,590	$ 1,337,213
Used Vehicle Retail Sales	780,570	660,927
Used Vehicle Wholesale Sales	104,029	104,157
New and Used Vehicle Sales	2,398,189	2,102,297
Vehicle parts sales	85,196	74,665
Maintenance and Repair Sales	264,319	245,033
Parts And Service Sales	349,515	319,698
Financial Services Revenue	112,322	96,834
Revenues	$ 2,860,026	$ 2,518,829

Maintenance and Repair Sales

No definition available.

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- Definition

Aggregate revenue recognized during the period derived from new vehicles sold to retail customers. Revenues from new vehicle retail sales are recognized upon completion of the sale and delivery to the customer. Conditions to completing a sale include having an agreement with the customer, including pricing, and the sales price must be reasonably expected to be collected.

+ References

No definition available.

+ Details

Name:	gpi_NewVehicleRetailSales
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

New and Used Vehicle Sales

+ References

No definition available.

+ Details

Name:	gpi_NewandUsedVehicleSales
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate revenue recognized during the period derived from parts sold to retail and wholesale customers, as well as performance of vehicle services and repairs. Revenues from new vehicle retail sales are recognized upon completion of the sale and delivery to the customer. Conditions to completing a sale include having an agreement with the customer, including pricing, and the sales price must be reasonably expected to be collected.

+ References

No definition available.

+ Details

Name:	gpi_PartsAndServiceSales
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Period Type:	duration

- Definition

Aggregate revenue recognized during the period derived from used vehicles sold to retail customers. Revenues from new vehicle retail sales are recognized upon completion of the sale and delivery to the customer. Conditions to completing a sale include having an agreement with the customer, including pricing, and the sales price must be reasonably expected to be collected.

+ References

No definition available.

+ Details

Name:	gpi_UsedVehicleRetailSales
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate revenue recognized during the period derived from used vehicles sold to wholesale customers. Revenues from new vehicle retail sales are recognized upon completion of the sale and delivery to the customer. Conditions to completing a sale include having an agreement with the customer, including pricing, and the sales price must be reasonably expected to be collected.

+ References

No definition available.

+ Details

Name:	gpi_UsedVehicleWholesaleSales
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Vehicle parts sales

+ References

No definition available.

+ Details

Name:	gpi_Vehiclepartssales
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate financial services revenue and operating interest income earned during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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Period Type:	duration