XML 70 R54.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Summary of Significant Accounting Policies and Estimates - Cash and Cash Equivalents (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Accounting Policies [Abstract] |  |
Immediately available funds excluded from cash and cash equivalents | $ 33.7 | $ 109.0

X
- Definition Credit facility floor plan offset. + References No definition available. + Details
Name: | gpi_CreditFacilityFloorPlanOffset
Namespace Prefix: | gpi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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