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v3.20.4

Business and Summary of Significant Accounting Policies - Statements of Cash Flows (Details) | 12 Months Ended
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Dec. 31, 2020
Accounting Policies [Abstract] |
Percent of value of the vehicle financed by the company (up to) | 85.00%

X
- Definition Value of used vehicle inventory financed + References No definition available. + Details
Name: | gpi_ValueOfUsedVehicleInventoryFinanced
Namespace Prefix: | gpi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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