XML 31 R53.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

Business and Summary of Significant Accounting Policies and Estimates - Goodwill (Details)	12 Months Ended
	Dec. 31, 2019 geographic_region
Accounting Policies [Abstract]
Number of geographic regions	3

X

- Definition

Number of geographic regions

+ References

No definition available.

+ Details

Name:	gpi_NumberOfGeographicRegions
Namespace Prefix:	gpi_
Data Type:	xbrli:integerItemType
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