Credit Facilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Outstanding balances under financing arrangements
Floorplan Offset	$ (81,996)	$ (112,261)
Floorplan notes payable - manufacturer affiliates	$ 301,670	$ 211,965

Amounts payable for the financing of specific new vehicle inventory with Ford Motor Credit Company, the financing of new and used vehicle inventory in the United Kingdom with BMW Financial Services and the financing of rental vehicle inventory with several other manufacturers. Payments on floor plan notes payable are generally due as the vehicles are sold.

No definition available.

Name:	gpi_FloorplanNotesPayableManufacturerAffiliates
Namespace Prefix:	gpi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant