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Consolidated Statement of Stockholders' Equity (Parenthetical)	3 Months Ended
	Sep. 30, 2014
3.00% Convertible Notes [Member]
Convertible senior notes stated rate	3.00%
2.25% Convertible Notes [Member]
Convertible senior notes stated rate	2.25%

X

- Definition

Equity component convertible note rate.

+ References

No definition available.

+ Details

Name:	gpi_EquityComponentConvertibleNoteRate
Namespace Prefix:	gpi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration